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 $249.48   13.422%   $282.9652   $282.97   $282.95   $283.00  
  Purchase #2 $233.56   4.708%   $244.556   $244.56   $244.55   $244.60  
  Purchase #3 $157.63   4.734%   $165.0922   $165.09   $165.10   $165.10  
  Purchase #4 $22.28   11.758%   $24.8997   $24.90   $24.90   $24.90  
  Purchase #5 $212.93   6.137%   $225.9975   $226.00   $226.00   $226.00  
  Purchase #6 $214.46   9.193%   $234.1753   $234.18   $234.20   $234.20  
  Purchase #7 $12.43   10.555%   $13.742   $13.74   $13.75   $13.70  
  7 purchase totals = $1,102.77       $1,191.4279   $1,191.44   $1,191.45   $1,191.50