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 $193.63   5.182%   $203.6639   $203.66   $203.65   $203.70  
  Purchase #2 $170.86   5.327%   $179.9617   $179.96   $179.95   $180.00  
  Purchase #3 $211.55   10.628%   $234.0335   $234.03   $234.05   $234.00  
  Purchase #4 $33.62   11.582%   $37.5139   $37.51   $37.50   $37.50  
  Purchase #5 $24.45   13.174%   $27.671   $27.67   $27.65   $27.70  
  Purchase #6 $207.32   4.746%   $217.1594   $217.16   $217.15   $217.20  
  Purchase #7 $51.56   5.858%   $54.5804   $54.58   $54.60   $54.60  
  7 purchase totals = $892.99       $954.5838   $954.57   $954.55   $954.70