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 $103.30   13.203%   $116.9387   $116.94   $116.95   $116.90  
  Purchase #2 $93.36   13.375%   $105.8469   $105.85   $105.85   $105.80  
  Purchase #3 $176.60   10.397%   $194.9611   $194.96   $194.95   $195.00  
  Purchase #4 $15.82   6.178%   $16.7974   $16.80   $16.80   $16.80  
  Purchase #5 $222.94   8.797%   $242.552   $242.55   $242.55   $242.60  
  Purchase #6 $160.73   12.388%   $180.6412   $180.64   $180.65   $180.60  
  Purchase #7 $175.58   12.746%   $197.9594   $197.96   $197.95   $198.00  
  7 purchase totals = $948.33       $1,055.6967   $1,055.70   $1,055.70   $1,055.70