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 $53.51   12.189%   $60.0323   $60.03   $60.05   $60.00  
  Purchase #2 $68.25   12.306%   $76.6488   $76.65   $76.65   $76.60  
  Purchase #3 $61.84   10.723%   $68.4711   $68.47   $68.45   $68.50  
  Purchase #4 $155.53   12.132%   $174.3989   $174.40   $174.40   $174.40  
  Purchase #5 $214.51   4.328%   $223.794   $223.79   $223.80   $223.80  
  Purchase #6 $132.98   11.861%   $148.7528   $148.75   $148.75   $148.80  
  Purchase #7 $55.46   7.301%   $59.5091   $59.51   $59.50   $59.50  
  7 purchase totals = $742.08       $811.6070   $811.60   $811.60   $811.60