Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $181.48   4.636%   $189.8934   $189.89   $189.90   $189.90  
  Purchase #2 $199.98   4.561%   $209.1011   $209.10   $209.10   $209.10  
  Purchase #3 $183.77   4.386%   $191.8302   $191.83   $191.85   $191.80  
  Purchase #4 $134.84   7.294%   $144.6752   $144.68   $144.70   $144.70  
  Purchase #5 $193.67   13.731%   $220.2628   $220.26   $220.25   $220.30  
  Purchase #6 $178.30   7.564%   $191.7866   $191.79   $191.80   $191.80  
  Purchase #7 $112.87   12.451%   $126.9234   $126.92   $126.90   $126.90  
  7 purchase totals = $1,184.91       $1,274.4727   $1,274.47   $1,274.50   $1,274.50