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 $116.58   11.179%   $129.6125   $129.61   $129.60   $129.60  
  Purchase #2 $224.85   12.494%   $252.9428   $252.94   $252.95   $252.90  
  Purchase #3 $59.32   6.202%   $62.999   $63.00   $63.00   $63.00  
  Purchase #4 $157.68   6.679%   $168.2114   $168.21   $168.20   $168.20  
  Purchase #5 $209.50   7.784%   $225.8075   $225.81   $225.80   $225.80  
  Purchase #6 $242.74   4.688%   $254.1197   $254.12   $254.10   $254.10  
  Purchase #7 $116.39   3.286%   $120.2146   $120.21   $120.20   $120.20  
  7 purchase totals = $1,127.06       $1,213.9075   $1,213.90   $1,213.85   $1,213.80