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 $176.54   10.385%   $194.8737   $194.87   $194.85   $194.90  
  Purchase #2 $153.48   5.666%   $162.1762   $162.18   $162.20   $162.20  
  Purchase #3 $201.58   4.301%   $210.25   $210.25   $210.25   $210.30  
  Purchase #4 $91.51   9.752%   $100.4341   $100.43   $100.45   $100.40  
  Purchase #5 $29.46   5.554%   $31.0962   $31.10   $31.10   $31.10  
  Purchase #6 $236.25   5.631%   $249.5532   $249.55   $249.55   $249.60  
  Purchase #7 $206.74   6.746%   $220.6867   $220.69   $220.70   $220.70  
  7 purchase totals = $1,095.56       $1,169.0701   $1,169.07   $1,169.10   $1,169.20