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 $140.51   8.211%   $152.0473   $152.05   $152.05   $152.00  
  Purchase #2 $112.38   9.304%   $122.8358   $122.84   $122.85   $122.80  
  Purchase #3 $99.71   12.274%   $111.9484   $111.95   $111.95   $111.90  
  Purchase #4 $205.93   8.632%   $223.7059   $223.71   $223.70   $223.70  
  Purchase #5 $214.57   5.664%   $226.7232   $226.72   $226.70   $226.70  
  Purchase #6 $10.82   3.666%   $11.2167   $11.22   $11.20   $11.20  
  Purchase #7 $87.74   12.670%   $98.8567   $98.86   $98.85   $98.90  
  7 purchase totals = $871.66       $947.3340   $947.35   $947.30   $947.20