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 $178.61   10.643%   $197.6195   $197.62   $197.60   $197.60  
  Purchase #2 $51.50   12.528%   $57.9519   $57.95   $57.95   $58.00  
  Purchase #3 $96.31   7.494%   $103.5275   $103.53   $103.55   $103.50  
  Purchase #4 $89.60   7.398%   $96.2286   $96.23   $96.25   $96.20  
  Purchase #5 $245.64   11.245%   $273.2622   $273.26   $273.25   $273.30  
  Purchase #6 $174.44   6.524%   $185.8205   $185.82   $185.80   $185.80  
  Purchase #7 $36.48   7.563%   $39.239   $39.24   $39.25   $39.20  
  7 purchase totals = $872.58       $953.6492   $953.65   $953.65   $953.60