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 $63.73   11.570%   $71.1036   $71.10   $71.10   $71.10  
  Purchase #2 $203.46   7.329%   $218.3716   $218.37   $218.35   $218.40  
  Purchase #3 $95.49   12.566%   $107.4893   $107.49   $107.50   $107.50  
  Purchase #4 $137.33   11.345%   $152.9101   $152.91   $152.90   $152.90  
  Purchase #5 $22.88   7.623%   $24.6241   $24.62   $24.60   $24.60  
  Purchase #6 $218.47   6.130%   $231.8622   $231.86   $231.85   $231.90  
  Purchase #7 $129.38   8.500%   $140.3773   $140.38   $140.40   $140.40  
  7 purchase totals = $870.74       $946.7382   $946.73   $946.70   $946.80