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 $219.45   8.521%   $238.1493   $238.15   $238.15   $238.10  
  Purchase #2 $170.86   13.154%   $193.3349   $193.33   $193.35   $193.30  
  Purchase #3 $74.94   5.235%   $78.8631   $78.86   $78.85   $78.90  
  Purchase #4 $208.63   4.778%   $218.5983   $218.60   $218.60   $218.60  
  Purchase #5 $245.38   4.723%   $256.9693   $256.97   $256.95   $257.00  
  Purchase #6 $246.63   4.780%   $258.4189   $258.42   $258.40   $258.40  
  Purchase #7 $10.36   6.610%   $11.0448   $11.04   $11.05   $11.00  
  7 purchase totals = $1,176.25       $1,255.3786   $1,255.37   $1,255.35   $1,255.30