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 $94.83   3.512%   $98.1604   $98.16   $98.15   $98.20  
  Purchase #2 $90.94   3.256%   $93.901   $93.90   $93.90   $93.90  
  Purchase #3 $116.37   6.778%   $124.2576   $124.26   $124.25   $124.30  
  Purchase #4 $151.52   12.386%   $170.2873   $170.29   $170.30   $170.30  
  Purchase #5 $35.47   3.354%   $36.6597   $36.66   $36.65   $36.70  
  Purchase #6 $66.61   9.311%   $72.8121   $72.81   $72.80   $72.80  
  Purchase #7 $75.81   11.363%   $84.4243   $84.42   $84.40   $84.40  
  7 purchase totals = $631.55       $680.5024   $680.50   $680.45   $680.60