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 $203.67   8.165%   $220.2997   $220.30   $220.30   $220.30  
  Purchase #2 $151.64   5.302%   $159.68   $159.68   $159.70   $159.70  
  Purchase #3 $30.78   11.493%   $34.3175   $34.32   $34.30   $34.30  
  Purchase #4 $179.97   6.217%   $191.1587   $191.16   $191.15   $191.20  
  Purchase #5 $98.90   11.616%   $110.3882   $110.39   $110.40   $110.40  
  Purchase #6 $140.85   11.765%   $157.421   $157.42   $157.40   $157.40  
  Purchase #7 $206.77   5.593%   $218.3346   $218.33   $218.35   $218.30  
  7 purchase totals = $1,012.58       $1,091.5997   $1,091.60   $1,091.60   $1,091.60