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 $34.64   9.528%   $37.9405   $37.94   $37.95   $37.90  
  Purchase #2 $210.99   13.491%   $239.4547   $239.45   $239.45   $239.50  
  Purchase #3 $63.55   5.397%   $66.9798   $66.98   $67.00   $67.00  
  Purchase #4 $173.87   5.412%   $183.2798   $183.28   $183.30   $183.30  
  Purchase #5 $99.36   5.802%   $105.1249   $105.12   $105.10   $105.10  
  Purchase #6 $219.45   11.459%   $244.5968   $244.60   $244.60   $244.60  
  Purchase #7 $183.67   4.869%   $192.6129   $192.61   $192.60   $192.60  
  7 purchase totals = $985.53       $1,069.9894   $1,069.98   $1,070.00   $1,070.00