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 $246.92   3.151%   $254.7004   $254.70   $254.70   $254.70  
  Purchase #2 $139.66   8.286%   $151.2322   $151.23   $151.25   $151.20  
  Purchase #3 $117.29   9.704%   $128.6718   $128.67   $128.65   $128.70  
  Purchase #4 $16.38   4.848%   $17.1741   $17.17   $17.15   $17.20  
  Purchase #5 $30.73   11.325%   $34.2102   $34.21   $34.20   $34.20  
  Purchase #6 $168.61   6.761%   $180.0097   $180.01   $180.00   $180.00  
  Purchase #7 $247.92   3.510%   $256.622   $256.62   $256.60   $256.60  
  7 purchase totals = $967.51       $1,022.6204   $1,022.61   $1,022.55   $1,022.60