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 $148.71   5.558%   $156.9753   $156.98   $157.00   $157.00  
  Purchase #2 $180.36   13.674%   $205.0224   $205.02   $205.00   $205.00  
  Purchase #3 $93.76   8.729%   $101.9443   $101.94   $101.95   $101.90  
  Purchase #4 $155.87   10.136%   $171.669   $171.67   $171.65   $171.70  
  Purchase #5 $181.27   5.816%   $191.8127   $191.81   $191.80   $191.80  
  Purchase #6 $118.39   11.756%   $132.3079   $132.31   $132.30   $132.30  
  Purchase #7 $34.61   6.226%   $36.7648   $36.76   $36.75   $36.80  
  7 purchase totals = $912.97       $996.4964   $996.49   $996.45   $996.50