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 $14.86   11.411%   $16.5557   $16.56   $16.55   $16.60  
  Purchase #2 $152.96   3.587%   $158.4467   $158.45   $158.45   $158.40  
  Purchase #3 $49.75   11.841%   $55.6409   $55.64   $55.65   $55.60  
  Purchase #4 $198.85   4.386%   $207.5716   $207.57   $207.55   $207.60  
  Purchase #5 $220.85   7.365%   $237.1156   $237.12   $237.10   $237.10  
  Purchase #6 $15.78   5.129%   $16.5894   $16.59   $16.60   $16.60  
  Purchase #7 $186.62   9.266%   $203.9122   $203.91   $203.90   $203.90  
  7 purchase totals = $839.67       $895.8321   $895.84   $895.80   $895.80