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 $65.31   6.475%   $69.5388   $69.54   $69.55   $69.50  
  Purchase #2 $32.87   8.646%   $35.7119   $35.71   $35.70   $35.70  
  Purchase #3 $193.98   11.348%   $215.9929   $215.99   $216.00   $216.00  
  Purchase #4 $140.67   8.459%   $152.5693   $152.57   $152.55   $152.60  
  Purchase #5 $118.78   8.666%   $129.0735   $129.07   $129.05   $129.10  
  Purchase #6 $130.48   13.575%   $148.1927   $148.19   $148.20   $148.20  
  Purchase #7 $14.63   10.277%   $16.1335   $16.13   $16.15   $16.10  
  7 purchase totals = $696.72       $767.2126   $767.20   $767.20   $767.20