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 $227.98   7.268%   $244.5496   $244.55   $244.55   $244.50  
  Purchase #2 $158.74   11.688%   $177.2935   $177.29   $177.30   $177.30  
  Purchase #3 $49.74   5.676%   $52.5632   $52.56   $52.55   $52.60  
  Purchase #4 $181.29   12.128%   $203.2769   $203.28   $203.30   $203.30  
  Purchase #5 $176.48   9.650%   $193.5103   $193.51   $193.50   $193.50  
  Purchase #6 $47.97   5.164%   $50.4472   $50.45   $50.45   $50.40  
  Purchase #7 $89.43   13.239%   $101.2696   $101.27   $101.25   $101.30  
  7 purchase totals = $931.63       $1,022.9103   $1,022.91   $1,022.90   $1,022.90