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 $58.76   12.853%   $66.3124   $66.31   $66.30   $66.30  
  Purchase #2 $66.70   9.480%   $73.0232   $73.02   $73.00   $73.00  
  Purchase #3 $44.69   6.559%   $47.6212   $47.62   $47.60   $47.60  
  Purchase #4 $241.97   7.586%   $260.3258   $260.33   $260.35   $260.30  
  Purchase #5 $135.26   8.661%   $146.9749   $146.97   $146.95   $147.00  
  Purchase #6 $186.61   13.553%   $211.9013   $211.90   $211.90   $211.90  
  Purchase #7 $43.65   10.547%   $48.2538   $48.25   $48.25   $48.30  
  7 purchase totals = $777.64       $854.4126   $854.40   $854.35   $854.40