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 $55.87   12.311%   $62.7482   $62.75   $62.75   $62.70  
  Purchase #2 $74.33   8.459%   $80.6176   $80.62   $80.60   $80.60  
  Purchase #3 $182.29   5.303%   $191.9568   $191.96   $191.95   $192.00  
  Purchase #4 $215.49   8.437%   $233.6709   $233.67   $233.65   $233.70  
  Purchase #5 $125.46   10.139%   $138.1804   $138.18   $138.20   $138.20  
  Purchase #6 $244.44   6.486%   $260.2944   $260.29   $260.30   $260.30  
  Purchase #7 $34.64   5.526%   $36.5542   $36.55   $36.55   $36.60  
  7 purchase totals = $932.52       $1,004.0225   $1,004.02   $1,004.00   $1,004.10