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 $60.43   9.717%   $66.302   $66.30   $66.30   $66.30  
  Purchase #2 $56.96   3.262%   $58.818   $58.82   $58.80   $58.80  
  Purchase #3 $65.82   13.746%   $74.8676   $74.87   $74.85   $74.90  
  Purchase #4 $110.40   7.557%   $118.7429   $118.74   $118.75   $118.70  
  Purchase #5 $25.93   10.471%   $28.6451   $28.65   $28.65   $28.60  
  Purchase #6 $25.27   3.469%   $26.1466   $26.15   $26.15   $26.10  
  Purchase #7 $205.30   7.705%   $221.1184   $221.12   $221.10   $221.10  
  7 purchase totals = $550.11       $594.6406   $594.65   $594.60   $594.50