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 $60.71   10.760%   $67.2424   $67.24   $67.25   $67.20  
  Purchase #2 $210.35   7.847%   $226.8562   $226.86   $226.85   $226.90  
  Purchase #3 $111.91   12.504%   $125.9032   $125.90   $125.90   $125.90  
  Purchase #4 $193.63   8.553%   $210.1912   $210.19   $210.20   $210.20  
  Purchase #5 $38.37   8.121%   $41.486   $41.49   $41.50   $41.50  
  Purchase #6 $192.36   10.414%   $212.3924   $212.39   $212.40   $212.40  
  Purchase #7 $164.67   13.302%   $186.5744   $186.57   $186.55   $186.60  
  7 purchase totals = $972.00       $1,070.6458   $1,070.64   $1,070.65   $1,070.70