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 $116.75   6.831%   $124.7252   $124.73   $124.75   $124.70  
  Purchase #2 $9.40   7.557%   $10.1104   $10.11   $10.10   $10.10  
  Purchase #3 $82.87   6.128%   $87.9483   $87.95   $87.95   $87.90  
  Purchase #4 $196.42   3.490%   $203.2751   $203.28   $203.30   $203.30  
  Purchase #5 $27.96   8.834%   $30.43   $30.43   $30.45   $30.40  
  Purchase #6 $120.52   9.607%   $132.0984   $132.10   $132.10   $132.10  
  Purchase #7 $117.38   6.685%   $125.2269   $125.23   $125.25   $125.20  
  7 purchase totals = $671.30       $713.8143   $713.83   $713.90   $713.70