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 $118.93   5.387%   $125.3368   $125.34   $125.35   $125.30  
  Purchase #2 $211.79   4.205%   $220.6958   $220.70   $220.70   $220.70  
  Purchase #3 $172.90   11.430%   $192.6625   $192.66   $192.65   $192.70  
  Purchase #4 $132.91   6.687%   $141.7977   $141.80   $141.80   $141.80  
  Purchase #5 $166.86   13.444%   $189.2927   $189.29   $189.30   $189.30  
  Purchase #6 $73.97   4.367%   $77.2003   $77.20   $77.20   $77.20  
  Purchase #7 $113.66   8.502%   $123.3234   $123.32   $123.30   $123.30  
  7 purchase totals = $991.02       $1,070.3092   $1,070.31   $1,070.30   $1,070.30