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 $70.97   8.492%   $76.9968   $77.00   $77.00   $77.00  
  Purchase #2 $75.49   8.423%   $81.8485   $81.85   $81.85   $81.80  
  Purchase #3 $106.30   12.541%   $119.6311   $119.63   $119.65   $119.60  
  Purchase #4 $177.45   10.215%   $195.5765   $195.58   $195.60   $195.60  
  Purchase #5 $236.81   11.513%   $264.0739   $264.07   $264.05   $264.10  
  Purchase #6 $118.85   10.304%   $131.0963   $131.10   $131.10   $131.10  
  Purchase #7 $143.27   3.564%   $148.3761   $148.38   $148.40   $148.40  
  7 purchase totals = $929.14       $1,017.5992   $1,017.61   $1,017.65   $1,017.60