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 $24.38   11.388%   $27.1564   $27.16   $27.15   $27.20  
  Purchase #2 $161.84   12.553%   $182.1558   $182.16   $182.15   $182.20  
  Purchase #3 $203.88   10.188%   $224.6513   $224.65   $224.65   $224.70  
  Purchase #4 $137.44   5.305%   $144.7312   $144.73   $144.75   $144.70  
  Purchase #5 $119.54   3.728%   $123.9965   $124.00   $124.00   $124.00  
  Purchase #6 $135.47   8.682%   $147.2315   $147.23   $147.25   $147.20  
  Purchase #7 $139.39   13.562%   $158.2941   $158.29   $158.30   $158.30  
  7 purchase totals = $921.94       $1,008.2168   $1,008.22   $1,008.25   $1,008.30