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 $233.26   5.740%   $246.6491   $246.65   $246.65   $246.60  
  Purchase #2 $225.38   11.223%   $250.6744   $250.67   $250.65   $250.70  
  Purchase #3 $247.50   8.346%   $268.1564   $268.16   $268.15   $268.20  
  Purchase #4 $141.94   4.429%   $148.2265   $148.23   $148.25   $148.20  
  Purchase #5 $223.54   4.327%   $233.2126   $233.21   $233.20   $233.20  
  Purchase #6 $182.35   11.563%   $203.4351   $203.44   $203.45   $203.40  
  Purchase #7 $228.67   5.573%   $241.4138   $241.41   $241.40   $241.40  
  7 purchase totals = $1,482.64       $1,591.7679   $1,591.77   $1,591.75   $1,591.70