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 $69.43   6.177%   $73.7187   $73.72   $73.70   $73.70  
  Purchase #2 $29.60   8.219%   $32.0328   $32.03   $32.05   $32.00  
  Purchase #3 $228.40   5.549%   $241.0739   $241.07   $241.05   $241.10  
  Purchase #4 $63.39   6.167%   $67.2993   $67.30   $67.30   $67.30  
  Purchase #5 $12.80   9.420%   $14.0058   $14.01   $14.00   $14.00  
  Purchase #6 $222.74   9.797%   $244.5618   $244.56   $244.55   $244.60  
  Purchase #7 $30.68   5.216%   $32.2803   $32.28   $32.30   $32.30  
  7 purchase totals = $657.04       $704.9726   $704.97   $704.95   $705.00