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 $246.68   8.514%   $267.6823   $267.68   $267.70   $267.70  
  Purchase #2 $175.36   9.181%   $191.4598   $191.46   $191.45   $191.50  
  Purchase #3 $183.65   6.251%   $195.13   $195.13   $195.15   $195.10  
  Purchase #4 $104.61   11.230%   $116.3577   $116.36   $116.35   $116.40  
  Purchase #5 $72.74   5.306%   $76.5996   $76.60   $76.60   $76.60  
  Purchase #6 $21.75   6.829%   $23.2353   $23.24   $23.25   $23.20  
  Purchase #7 $119.60   8.561%   $129.839   $129.84   $129.85   $129.80  
  7 purchase totals = $924.39       $1,000.3037   $1,000.31   $1,000.35   $1,000.30