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 $89.31   5.775%   $94.4677   $94.47   $94.45   $94.50  
  Purchase #2 $185.71   11.426%   $206.9292   $206.93   $206.95   $206.90  
  Purchase #3 $48.55   11.580%   $54.1721   $54.17   $54.15   $54.20  
  Purchase #4 $73.47   13.147%   $83.1291   $83.13   $83.15   $83.10  
  Purchase #5 $87.98   9.285%   $96.1489   $96.15   $96.15   $96.10  
  Purchase #6 $212.66   12.837%   $239.9592   $239.96   $239.95   $240.00  
  Purchase #7 $83.96   9.445%   $91.89   $91.89   $91.90   $91.90  
  7 purchase totals = $781.64       $866.6962   $866.70   $866.70   $866.70