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 $43.66   5.597%   $46.1037   $46.10   $46.10   $46.10  
  Purchase #2 $205.73   11.502%   $229.3931   $229.39   $229.40   $229.40  
  Purchase #3 $248.70   7.473%   $267.2854   $267.29   $267.30   $267.30  
  Purchase #4 $215.88   3.530%   $223.5006   $223.50   $223.50   $223.50  
  Purchase #5 $54.39   7.869%   $58.6699   $58.67   $58.65   $58.70  
  Purchase #6 $141.95   13.646%   $161.3205   $161.32   $161.30   $161.30  
  Purchase #7 $15.90   4.506%   $16.6165   $16.62   $16.60   $16.60  
  7 purchase totals = $926.21       $1,002.8897   $1,002.89   $1,002.85   $1,002.90