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 $70.91   6.516%   $75.5305   $75.53   $75.55   $75.50  
  Purchase #2 $224.73   6.462%   $239.2521   $239.25   $239.25   $239.30  
  Purchase #3 $97.45   8.125%   $105.3678   $105.37   $105.35   $105.40  
  Purchase #4 $117.68   13.826%   $133.9504   $133.95   $133.95   $134.00  
  Purchase #5 $58.96   11.216%   $65.573   $65.57   $65.55   $65.60  
  Purchase #6 $168.39   7.316%   $180.7094   $180.71   $180.70   $180.70  
  Purchase #7 $200.58   9.335%   $219.3041   $219.30   $219.30   $219.30  
  7 purchase totals = $938.70       $1,019.6873   $1,019.68   $1,019.65   $1,019.80