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 $76.71   9.273%   $83.8233   $83.82   $83.80   $83.80  
  Purchase #2 $246.60   11.669%   $275.3758   $275.38   $275.40   $275.40  
  Purchase #3 $196.27   11.277%   $218.4034   $218.40   $218.40   $218.40  
  Purchase #4 $169.70   5.713%   $179.395   $179.40   $179.40   $179.40  
  Purchase #5 $156.75   4.441%   $163.7113   $163.71   $163.70   $163.70  
  Purchase #6 $157.86   11.297%   $175.6934   $175.69   $175.70   $175.70  
  Purchase #7 $197.35   8.324%   $213.7774   $213.78   $213.80   $213.80  
  7 purchase totals = $1,201.24       $1,310.1796   $1,310.18   $1,310.20   $1,310.20