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 $43.39   6.644%   $46.2728   $46.27   $46.25   $46.30  
  Purchase #2 $218.98   9.518%   $239.8225   $239.82   $239.80   $239.80  
  Purchase #3 $138.88   12.795%   $156.6497   $156.65   $156.65   $156.60  
  Purchase #4 $190.71   7.460%   $204.937   $204.94   $204.95   $204.90  
  Purchase #5 $248.90   13.145%   $281.6179   $281.62   $281.60   $281.60  
  Purchase #6 $239.66   3.346%   $247.679   $247.68   $247.70   $247.70  
  Purchase #7 $231.44   6.671%   $246.8794   $246.88   $246.90   $246.90  
  7 purchase totals = $1,311.96       $1,423.8583   $1,423.86   $1,423.85   $1,423.80