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 $95.80   11.764%   $107.0699   $107.07   $107.05   $107.10  
  Purchase #2 $170.69   12.442%   $191.9272   $191.93   $191.95   $191.90  
  Purchase #3 $161.25   5.663%   $170.3816   $170.38   $170.40   $170.40  
  Purchase #4 $85.40   6.180%   $90.6777   $90.68   $90.70   $90.70  
  Purchase #5 $247.59   5.261%   $260.6157   $260.62   $260.60   $260.60  
  Purchase #6 $48.89   8.841%   $53.2124   $53.21   $53.20   $53.20  
  Purchase #7 $22.89   5.508%   $24.1508   $24.15   $24.15   $24.20  
  7 purchase totals = $832.51       $898.0353   $898.04   $898.05   $898.10