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 $66.57   13.786%   $75.7473   $75.75   $75.75   $75.70  
  Purchase #2 $201.74   10.193%   $222.3034   $222.30   $222.30   $222.30  
  Purchase #3 $52.29   10.670%   $57.8693   $57.87   $57.85   $57.90  
  Purchase #4 $156.67   8.393%   $169.8193   $169.82   $169.80   $169.80  
  Purchase #5 $215.76   7.104%   $231.0876   $231.09   $231.10   $231.10  
  Purchase #6 $158.76   7.806%   $171.1528   $171.15   $171.15   $171.20  
  Purchase #7 $191.27   11.772%   $213.7863   $213.79   $213.80   $213.80  
  7 purchase totals = $1,043.06       $1,141.7660   $1,141.77   $1,141.75   $1,141.80