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 $94.87   3.165%   $97.8726   $97.87   $97.85   $97.90  
  Purchase #2 $151.55   11.151%   $168.4493   $168.45   $168.45   $168.40  
  Purchase #3 $56.34   8.190%   $60.9542   $60.95   $60.95   $61.00  
  Purchase #4 $77.37   3.330%   $79.9464   $79.95   $79.95   $79.90  
  Purchase #5 $234.68   12.657%   $264.3834   $264.38   $264.40   $264.40  
  Purchase #6 $110.85   11.871%   $124.009   $124.01   $124.00   $124.00  
  Purchase #7 $80.41   11.580%   $89.7215   $89.72   $89.70   $89.70  
  7 purchase totals = $806.07       $885.3364   $885.33   $885.30   $885.30