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 $82.94   12.442%   $93.2594   $93.26   $93.25   $93.30  
  Purchase #2 $187.69   7.425%   $201.626   $201.63   $201.65   $201.60  
  Purchase #3 $217.56   6.231%   $231.1162   $231.12   $231.10   $231.10  
  Purchase #4 $234.97   10.480%   $259.5949   $259.59   $259.60   $259.60  
  Purchase #5 $34.50   4.577%   $36.0791   $36.08   $36.10   $36.10  
  Purchase #6 $226.89   10.359%   $250.3935   $250.39   $250.40   $250.40  
  Purchase #7 $174.35   9.468%   $190.8575   $190.86   $190.85   $190.90  
  7 purchase totals = $1,158.90       $1,262.9266   $1,262.93   $1,262.95   $1,263.00