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 $195.70   11.149%   $217.5186   $217.52   $217.50   $217.50  
  Purchase #2 $92.29   6.112%   $97.9308   $97.93   $97.95   $97.90  
  Purchase #3 $113.83   11.385%   $126.7895   $126.79   $126.80   $126.80  
  Purchase #4 $92.92   10.130%   $102.3328   $102.33   $102.35   $102.30  
  Purchase #5 $38.67   8.156%   $41.8239   $41.82   $41.80   $41.80  
  Purchase #6 $168.77   5.289%   $177.6962   $177.70   $177.70   $177.70  
  Purchase #7 $181.46   3.867%   $188.4771   $188.48   $188.50   $188.50  
  7 purchase totals = $883.64       $952.5689   $952.57   $952.60   $952.50