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 $95.59   7.494%   $102.7535   $102.75   $102.75   $102.80  
  Purchase #2 $84.32   10.215%   $92.9333   $92.93   $92.95   $92.90  
  Purchase #3 $48.56   12.762%   $54.7572   $54.76   $54.75   $54.80  
  Purchase #4 $84.35   3.832%   $87.5823   $87.58   $87.60   $87.60  
  Purchase #5 $169.42   11.867%   $189.5251   $189.53   $189.55   $189.50  
  Purchase #6 $233.46   8.475%   $253.2457   $253.25   $253.25   $253.20  
  Purchase #7 $247.45   12.384%   $278.0942   $278.09   $278.10   $278.10  
  7 purchase totals = $963.15       $1,058.8913   $1,058.89   $1,058.95   $1,058.90