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 $54.89   7.764%   $59.1517   $59.15   $59.15   $59.20  
  Purchase #2 $230.98   13.701%   $262.6266   $262.63   $262.65   $262.60  
  Purchase #3 $17.61   7.632%   $18.954   $18.95   $18.95   $19.00  
  Purchase #4 $54.32   10.756%   $60.1627   $60.16   $60.15   $60.20  
  Purchase #5 $45.36   11.664%   $50.6508   $50.65   $50.65   $50.70  
  Purchase #6 $155.98   7.482%   $167.6504   $167.65   $167.65   $167.70  
  Purchase #7 $129.57   12.354%   $145.5771   $145.58   $145.60   $145.60  
  7 purchase totals = $688.71       $764.7733   $764.77   $764.80   $765.00