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 $32.54   6.434%   $34.6336   $34.63   $34.65   $34.60  
  Purchase #2 $129.55   5.449%   $136.6092   $136.61   $136.60   $136.60  
  Purchase #3 $199.67   12.258%   $224.1455   $224.15   $224.15   $224.10  
  Purchase #4 $153.25   5.530%   $161.7247   $161.72   $161.70   $161.70  
  Purchase #5 $73.83   6.280%   $78.4665   $78.47   $78.45   $78.50  
  Purchase #6 $216.62   5.847%   $229.2858   $229.29   $229.30   $229.30  
  Purchase #7 $15.75   7.486%   $16.929   $16.93   $16.95   $16.90  
  7 purchase totals = $821.21       $881.7943   $881.80   $881.80   $881.70