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 $244.60   7.737%   $263.5247   $263.52   $263.50   $263.50  
  Purchase #2 $53.98   8.145%   $58.3767   $58.38   $58.40   $58.40  
  Purchase #3 $136.73   4.631%   $143.062   $143.06   $143.05   $143.10  
  Purchase #4 $83.34   13.228%   $94.3642   $94.36   $94.35   $94.40  
  Purchase #5 $92.92   3.768%   $96.4212   $96.42   $96.40   $96.40  
  Purchase #6 $95.37   9.585%   $104.5112   $104.51   $104.50   $104.50  
  Purchase #7 $171.50   7.318%   $184.0504   $184.05   $184.05   $184.10  
  7 purchase totals = $878.44       $944.3104   $944.30   $944.25   $944.40