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 $61.56   7.729%   $66.318   $66.32   $66.30   $66.30  
  Purchase #2 $46.52   3.651%   $48.2184   $48.22   $48.20   $48.20  
  Purchase #3 $43.79   13.718%   $49.7971   $49.80   $49.80   $49.80  
  Purchase #4 $241.75   3.484%   $250.1726   $250.17   $250.15   $250.20  
  Purchase #5 $58.97   11.183%   $65.5646   $65.56   $65.55   $65.60  
  Purchase #6 $164.72   12.869%   $185.9178   $185.92   $185.90   $185.90  
  Purchase #7 $64.27   10.637%   $71.1064   $71.11   $71.10   $71.10  
  7 purchase totals = $681.58       $737.0949   $737.10   $737.00   $737.10