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 $56.61   10.694%   $62.6639   $62.66   $62.65   $62.70  
  Purchase #2 $31.52   4.563%   $32.9583   $32.96   $32.95   $33.00  
  Purchase #3 $249.27   3.576%   $258.1839   $258.18   $258.20   $258.20  
  Purchase #4 $134.72   11.160%   $149.7548   $149.75   $149.75   $149.80  
  Purchase #5 $66.97   9.628%   $73.4179   $73.42   $73.40   $73.40  
  Purchase #6 $220.42   9.320%   $240.9631   $240.96   $240.95   $241.00  
  Purchase #7 $101.90   7.761%   $109.8085   $109.81   $109.80   $109.80  
  7 purchase totals = $861.41       $927.7504   $927.74   $927.70   $927.90