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 $242.39   11.680%   $270.7012   $270.70   $270.70   $270.70  
  Purchase #2 $117.38   8.133%   $126.9265   $126.93   $126.95   $126.90  
  Purchase #3 $96.83   5.556%   $102.2099   $102.21   $102.20   $102.20  
  Purchase #4 $239.48   12.308%   $268.9552   $268.96   $268.95   $269.00  
  Purchase #5 $118.46   10.753%   $131.198   $131.20   $131.20   $131.20  
  Purchase #6 $161.48   6.277%   $171.6161   $171.62   $171.60   $171.60  
  Purchase #7 $215.61   12.441%   $242.434   $242.43   $242.45   $242.40  
  7 purchase totals = $1,191.63       $1,314.0409   $1,314.05   $1,314.05   $1,314.00