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 $213.89   9.799%   $234.8491   $234.85   $234.85   $234.80  
  Purchase #2 $35.50   7.352%   $38.11   $38.11   $38.10   $38.10  
  Purchase #3 $174.74   4.352%   $182.3447   $182.34   $182.35   $182.30  
  Purchase #4 $100.99   13.519%   $114.6428   $114.64   $114.65   $114.60  
  Purchase #5 $240.80   12.181%   $270.1318   $270.13   $270.15   $270.10  
  Purchase #6 $170.40   4.606%   $178.2486   $178.25   $178.25   $178.20  
  Purchase #7 $245.51   5.279%   $258.4705   $258.47   $258.45   $258.50  
  7 purchase totals = $1,181.83       $1,276.7975   $1,276.79   $1,276.80   $1,276.60