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 $51.92   10.268%   $57.2511   $57.25   $57.25   $57.30  
  Purchase #2 $231.53   6.717%   $247.0819   $247.08   $247.10   $247.10  
  Purchase #3 $147.41   4.180%   $153.5717   $153.57   $153.55   $153.60  
  Purchase #4 $68.67   6.251%   $72.9626   $72.96   $72.95   $73.00  
  Purchase #5 $215.30   6.719%   $229.766   $229.77   $229.75   $229.80  
  Purchase #6 $58.87   13.689%   $66.9287   $66.93   $66.95   $66.90  
  Purchase #7 $109.43   12.830%   $123.4699   $123.47   $123.45   $123.50  
  7 purchase totals = $883.13       $951.0319   $951.03   $951.00   $951.20