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 $160.58   9.616%   $176.0214   $176.02   $176.00   $176.00  
  Purchase #2 $32.27   4.363%   $33.6779   $33.68   $33.70   $33.70  
  Purchase #3 $243.55   5.433%   $256.7821   $256.78   $256.80   $256.80  
  Purchase #4 $115.76   10.563%   $127.9877   $127.99   $128.00   $128.00  
  Purchase #5 $72.99   9.203%   $79.7073   $79.71   $79.70   $79.70  
  Purchase #6 $125.91   4.408%   $131.4601   $131.46   $131.45   $131.50  
  Purchase #7 $182.67   13.823%   $207.9205   $207.92   $207.90   $207.90  
  7 purchase totals = $933.73       $1,013.5570   $1,013.56   $1,013.55   $1,013.60