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 $60.94   6.795%   $65.0809   $65.08   $65.10   $65.10  
  Purchase #2 $151.41   13.185%   $171.3734   $171.37   $171.35   $171.40  
  Purchase #3 $241.66   6.788%   $258.0639   $258.06   $258.05   $258.10  
  Purchase #4 $250.58   8.747%   $272.4982   $272.50   $272.50   $272.50  
  Purchase #5 $29.32   10.431%   $32.3784   $32.38   $32.40   $32.40  
  Purchase #6 $91.53   3.380%   $94.6237   $94.62   $94.60   $94.60  
  Purchase #7 $245.53   7.636%   $264.2787   $264.28   $264.30   $264.30  
  7 purchase totals = $1,070.97       $1,158.2972   $1,158.29   $1,158.30   $1,158.40