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 $241.66   11.650%   $269.8134   $269.81   $269.80   $269.80  
  Purchase #2 $110.42   12.561%   $124.2899   $124.29   $124.30   $124.30  
  Purchase #3 $27.33   13.754%   $31.089   $31.09   $31.10   $31.10  
  Purchase #4 $244.34   13.142%   $276.4512   $276.45   $276.45   $276.50  
  Purchase #5 $105.89   13.122%   $119.7849   $119.78   $119.80   $119.80  
  Purchase #6 $143.56   12.272%   $161.1777   $161.18   $161.20   $161.20  
  Purchase #7 $246.28   6.645%   $262.6453   $262.65   $262.65   $262.60  
  7 purchase totals = $1,119.48       $1,245.2514   $1,245.25   $1,245.30   $1,245.30