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 $134.36   8.295%   $145.5052   $145.51   $145.50   $145.50  
  Purchase #2 $223.47   6.216%   $237.3609   $237.36   $237.35   $237.40  
  Purchase #3 $8.25   3.250%   $8.5181   $8.52   $8.50   $8.50  
  Purchase #4 $88.62   10.260%   $97.7124   $97.71   $97.70   $97.70  
  Purchase #5 $196.33   13.762%   $223.3489   $223.35   $223.35   $223.30  
  Purchase #6 $200.89   12.838%   $226.6803   $226.68   $226.70   $226.70  
  Purchase #7 $149.40   7.750%   $160.9785   $160.98   $161.00   $161.00  
  7 purchase totals = $1,001.32       $1,100.1043   $1,100.11   $1,100.10   $1,100.10