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 $94.86   7.643%   $102.1101   $102.11   $102.10   $102.10  
  Purchase #2 $202.34   4.454%   $211.3522   $211.35   $211.35   $211.40  
  Purchase #3 $199.60   7.576%   $214.7217   $214.72   $214.70   $214.70  
  Purchase #4 $149.48   5.355%   $157.4847   $157.48   $157.50   $157.50  
  Purchase #5 $250.57   13.622%   $284.7026   $284.70   $284.70   $284.70  
  Purchase #6 $247.25   11.571%   $275.8593   $275.86   $275.85   $275.90  
  Purchase #7 $20.38   10.450%   $22.5097   $22.51   $22.50   $22.50  
  7 purchase totals = $1,164.48       $1,268.7403   $1,268.73   $1,268.70   $1,268.80