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 $196.87   12.648%   $221.7701   $221.77   $221.75   $221.80  
  Purchase #2 $51.93   5.263%   $54.6631   $54.66   $54.65   $54.70  
  Purchase #3 $143.26   4.687%   $149.9746   $149.97   $149.95   $150.00  
  Purchase #4 $44.35   10.168%   $48.8595   $48.86   $48.85   $48.90  
  Purchase #5 $149.53   8.711%   $162.5556   $162.56   $162.55   $162.60  
  Purchase #6 $132.79   13.530%   $150.7565   $150.76   $150.75   $150.80  
  Purchase #7 $241.96   9.327%   $264.5276   $264.53   $264.55   $264.50  
  7 purchase totals = $960.69       $1,053.1070   $1,053.11   $1,053.05   $1,053.30