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 $248.86   7.786%   $268.2362   $268.24   $268.25   $268.20  
  Purchase #2 $54.82   6.448%   $58.3548   $58.35   $58.35   $58.40  
  Purchase #3 $185.39   5.527%   $195.6365   $195.64   $195.65   $195.60  
  Purchase #4 $242.31   7.624%   $260.7837   $260.78   $260.80   $260.80  
  Purchase #5 $238.48   12.815%   $269.0412   $269.04   $269.05   $269.00  
  Purchase #6 $136.96   9.695%   $150.2383   $150.24   $150.25   $150.20  
  Purchase #7 $62.96   13.397%   $71.3948   $71.39   $71.40   $71.40  
  7 purchase totals = $1,169.78       $1,273.6855   $1,273.68   $1,273.75   $1,273.60