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 $46.74   11.706%   $52.2114   $52.21   $52.20   $52.20  
  Purchase #2 $227.66   3.599%   $235.8535   $235.85   $235.85   $235.90  
  Purchase #3 $119.82   9.613%   $131.3383   $131.34   $131.35   $131.30  
  Purchase #4 $23.27   8.427%   $25.231   $25.23   $25.25   $25.20  
  Purchase #5 $179.58   13.358%   $203.5683   $203.57   $203.55   $203.60  
  Purchase #6 $69.96   12.139%   $78.4524   $78.45   $78.45   $78.50  
  Purchase #7 $129.39   7.338%   $138.8846   $138.88   $138.90   $138.90  
  7 purchase totals = $796.42       $865.5395   $865.53   $865.55   $865.60