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 $33.99   6.663%   $36.2548   $36.25   $36.25   $36.30  
  Purchase #2 $236.39   3.394%   $244.4131   $244.41   $244.40   $244.40  
  Purchase #3 $245.34   13.137%   $277.5703   $277.57   $277.55   $277.60  
  Purchase #4 $23.66   7.613%   $25.4612   $25.46   $25.45   $25.50  
  Purchase #5 $79.82   6.310%   $84.8566   $84.86   $84.85   $84.90  
  Purchase #6 $195.28   11.693%   $218.1141   $218.11   $218.10   $218.10  
  Purchase #7 $58.67   11.282%   $65.2891   $65.29   $65.30   $65.30  
  7 purchase totals = $873.15       $951.9592   $951.95   $951.90   $952.10