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 $85.95   6.206%   $91.2841   $91.28   $91.30   $91.30  
  Purchase #2 $101.44   7.753%   $109.3046   $109.30   $109.30   $109.30  
  Purchase #3 $173.81   12.750%   $195.9708   $195.97   $195.95   $196.00  
  Purchase #4 $16.60   12.760%   $18.7182   $18.72   $18.70   $18.70  
  Purchase #5 $216.50   8.270%   $234.4046   $234.40   $234.40   $234.40  
  Purchase #6 $109.41   8.784%   $119.0206   $119.02   $119.00   $119.00  
  Purchase #7 $57.93   7.587%   $62.3251   $62.33   $62.35   $62.30  
  7 purchase totals = $761.64       $831.0280   $831.02   $831.00   $831.00