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 $190.44   8.201%   $206.058   $206.06   $206.05   $206.10  
  Purchase #2 $76.88   3.361%   $79.4639   $79.46   $79.45   $79.50  
  Purchase #3 $222.82   13.405%   $252.689   $252.69   $252.70   $252.70  
  Purchase #4 $226.49   9.422%   $247.8299   $247.83   $247.85   $247.80  
  Purchase #5 $16.68   11.294%   $18.5638   $18.56   $18.55   $18.60  
  Purchase #6 $8.42   13.842%   $9.5855   $9.59   $9.60   $9.60  
  Purchase #7 $225.63   6.806%   $240.9864   $240.99   $241.00   $241.00  
  7 purchase totals = $967.36       $1,055.1765   $1,055.18   $1,055.20   $1,055.30