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 $188.35   8.254%   $203.8964   $203.90   $203.90   $203.90  
  Purchase #2 $240.32   11.859%   $268.8195   $268.82   $268.80   $268.80  
  Purchase #3 $54.71   8.709%   $59.4747   $59.47   $59.45   $59.50  
  Purchase #4 $177.77   13.129%   $201.1094   $201.11   $201.10   $201.10  
  Purchase #5 $247.89   3.548%   $256.6851   $256.69   $256.70   $256.70  
  Purchase #6 $204.92   6.827%   $218.9099   $218.91   $218.90   $218.90  
  Purchase #7 $245.65   3.308%   $253.7761   $253.78   $253.80   $253.80  
  7 purchase totals = $1,359.61       $1,462.6711   $1,462.68   $1,462.65   $1,462.70