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 $62.46   3.626%   $64.7248   $64.72   $64.70   $64.70  
  Purchase #2 $80.66   8.565%   $87.5685   $87.57   $87.55   $87.60  
  Purchase #3 $107.33   8.814%   $116.7901   $116.79   $116.80   $116.80  
  Purchase #4 $92.67   7.368%   $99.4979   $99.50   $99.50   $99.50  
  Purchase #5 $161.71   6.291%   $171.8832   $171.88   $171.90   $171.90  
  Purchase #6 $123.67   9.434%   $135.337   $135.34   $135.35   $135.30  
  Purchase #7 $111.79   6.652%   $119.2263   $119.23   $119.25   $119.20  
  7 purchase totals = $740.29       $795.0278   $795.03   $795.05   $795.00