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 $232.89   5.626%   $245.9924   $245.99   $246.00   $246.00  
  Purchase #2 $195.31   4.138%   $203.3919   $203.39   $203.40   $203.40  
  Purchase #3 $188.30   4.202%   $196.2124   $196.21   $196.20   $196.20  
  Purchase #4 $229.98   11.413%   $256.2276   $256.23   $256.25   $256.20  
  Purchase #5 $148.54   12.639%   $167.314   $167.31   $167.30   $167.30  
  Purchase #6 $86.50   12.453%   $97.2718   $97.27   $97.25   $97.30  
  Purchase #7 $202.47   7.734%   $218.129   $218.13   $218.15   $218.10  
  7 purchase totals = $1,283.99       $1,384.5391   $1,384.53   $1,384.55   $1,384.50