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 $201.94   6.269%   $214.5996   $214.60   $214.60   $214.60  
  Purchase #2 $69.94   13.380%   $79.298   $79.30   $79.30   $79.30  
  Purchase #3 $102.73   4.232%   $107.0775   $107.08   $107.10   $107.10  
  Purchase #4 $60.72   3.654%   $62.9387   $62.94   $62.95   $62.90  
  Purchase #5 $89.87   11.856%   $100.525   $100.53   $100.55   $100.50  
  Purchase #6 $194.49   6.317%   $206.7759   $206.78   $206.80   $206.80  
  Purchase #7 $97.71   8.679%   $106.1903   $106.19   $106.20   $106.20  
  7 purchase totals = $817.40       $877.4050   $877.42   $877.50   $877.40