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 $95.87   11.277%   $106.6813   $106.68   $106.70   $106.70  
  Purchase #2 $214.48   10.176%   $236.3055   $236.31   $236.30   $236.30  
  Purchase #3 $153.72   11.250%   $171.0135   $171.01   $171.00   $171.00  
  Purchase #4 $50.58   4.712%   $52.9633   $52.96   $52.95   $53.00  
  Purchase #5 $65.70   6.679%   $70.0881   $70.09   $70.10   $70.10  
  Purchase #6 $233.38   9.260%   $254.991   $254.99   $255.00   $255.00  
  Purchase #7 $138.31   7.339%   $148.4606   $148.46   $148.45   $148.50  
  7 purchase totals = $952.04       $1,040.5033   $1,040.50   $1,040.50   $1,040.60