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 $193.65   8.268%   $209.661   $209.66   $209.65   $209.70  
  Purchase #2 $235.67   10.158%   $259.6094   $259.61   $259.60   $259.60  
  Purchase #3 $126.42   13.547%   $143.5461   $143.55   $143.55   $143.50  
  Purchase #4 $49.67   4.145%   $51.7288   $51.73   $51.75   $51.70  
  Purchase #5 $110.54   8.497%   $119.9326   $119.93   $119.95   $119.90  
  Purchase #6 $104.96   9.837%   $115.2849   $115.28   $115.30   $115.30  
  Purchase #7 $32.34   6.626%   $34.4828   $34.48   $34.50   $34.50  
  7 purchase totals = $853.25       $934.2456   $934.24   $934.30   $934.20