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 $245.95   8.236%   $266.2064   $266.21   $266.20   $266.20  
  Purchase #2 $181.49   9.432%   $198.6081   $198.61   $198.60   $198.60  
  Purchase #3 $189.92   9.811%   $208.5531   $208.55   $208.55   $208.60  
  Purchase #4 $201.83   4.197%   $210.3008   $210.30   $210.30   $210.30  
  Purchase #5 $220.36   12.219%   $247.2858   $247.29   $247.30   $247.30  
  Purchase #6 $46.77   9.385%   $51.1594   $51.16   $51.15   $51.20  
  Purchase #7 $33.78   4.113%   $35.1694   $35.17   $35.15   $35.20  
  7 purchase totals = $1,120.10       $1,217.2830   $1,217.29   $1,217.25   $1,217.40