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 $218.55   11.846%   $244.4394   $244.44   $244.45   $244.40  
  Purchase #2 $233.26   7.420%   $250.5679   $250.57   $250.55   $250.60  
  Purchase #3 $73.63   12.422%   $82.7763   $82.78   $82.80   $82.80  
  Purchase #4 $92.95   5.318%   $97.8931   $97.89   $97.90   $97.90  
  Purchase #5 $185.69   9.515%   $203.3584   $203.36   $203.35   $203.40  
  Purchase #6 $236.42   11.498%   $263.6036   $263.60   $263.60   $263.60  
  Purchase #7 $30.50   10.846%   $33.808   $33.81   $33.80   $33.80  
  7 purchase totals = $1,071.00       $1,176.4467   $1,176.45   $1,176.45   $1,176.50