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 $87.34   11.486%   $97.3719   $97.37   $97.35   $97.40  
  Purchase #2 $70.50   7.252%   $75.6127   $75.61   $75.60   $75.60  
  Purchase #3 $82.81   3.465%   $85.6794   $85.68   $85.70   $85.70  
  Purchase #4 $65.90   7.132%   $70.6   $70.60   $70.60   $70.60  
  Purchase #5 $177.42   12.294%   $199.232   $199.23   $199.25   $199.20  
  Purchase #6 $121.44   3.528%   $125.7244   $125.72   $125.70   $125.70  
  Purchase #7 $247.99   9.780%   $272.2434   $272.24   $272.25   $272.20  
  7 purchase totals = $853.40       $926.4638   $926.45   $926.45   $926.40