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 $205.96   4.365%   $214.9502   $214.95   $214.95   $215.00  
  Purchase #2 $89.55   8.794%   $97.425   $97.43   $97.45   $97.40  
  Purchase #3 $5.29   11.663%   $5.907   $5.91   $5.90   $5.90  
  Purchase #4 $178.52   5.825%   $188.9188   $188.92   $188.90   $188.90  
  Purchase #5 $95.74   13.372%   $108.5424   $108.54   $108.55   $108.50  
  Purchase #6 $132.78   7.282%   $142.449   $142.45   $142.45   $142.40  
  Purchase #7 $151.53   12.518%   $170.4985   $170.50   $170.50   $170.50  
  7 purchase totals = $859.37       $928.6909   $928.70   $928.70   $928.60