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 $246.98   13.803%   $281.0706   $281.07   $281.05   $281.10  
  Purchase #2 $250.55   6.313%   $266.3672   $266.37   $266.35   $266.40  
  Purchase #3 $200.27   3.537%   $207.3535   $207.35   $207.35   $207.40  
  Purchase #4 $232.72   4.772%   $243.8254   $243.83   $243.85   $243.80  
  Purchase #5 $16.84   4.755%   $17.6407   $17.64   $17.65   $17.60  
  Purchase #6 $90.95   3.400%   $94.0423   $94.04   $94.05   $94.00  
  Purchase #7 $78.26   6.660%   $83.4721   $83.47   $83.45   $83.50  
  7 purchase totals = $1,116.57       $1,193.7718   $1,193.77   $1,193.75   $1,193.80