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 $68.64   13.676%   $78.0272   $78.03   $78.05   $78.00  
  Purchase #2 $223.42   7.503%   $240.1832   $240.18   $240.20   $240.20  
  Purchase #3 $228.62   7.407%   $245.5539   $245.55   $245.55   $245.60  
  Purchase #4 $246.65   8.740%   $268.2072   $268.21   $268.20   $268.20  
  Purchase #5 $67.49   7.542%   $72.5801   $72.58   $72.60   $72.60  
  Purchase #6 $118.78   5.250%   $125.016   $125.02   $125.00   $125.00  
  Purchase #7 $169.28   11.145%   $188.1463   $188.15   $188.15   $188.10  
  7 purchase totals = $1,122.88       $1,217.7139   $1,217.72   $1,217.75   $1,217.70