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 $92.93   12.719%   $104.7498   $104.75   $104.75   $104.70  
  Purchase #2 $230.34   12.544%   $259.2338   $259.23   $259.25   $259.20  
  Purchase #3 $111.57   5.702%   $117.9317   $117.93   $117.95   $117.90  
  Purchase #4 $172.33   12.749%   $194.3004   $194.30   $194.30   $194.30  
  Purchase #5 $60.95   8.208%   $65.9528   $65.95   $65.95   $66.00  
  Purchase #6 $138.46   4.352%   $144.4858   $144.49   $144.50   $144.50  
  Purchase #7 $117.73   11.730%   $131.5397   $131.54   $131.55   $131.50  
  7 purchase totals = $924.31       $1,018.1940   $1,018.19   $1,018.25   $1,018.10