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 $169.59   9.183%   $185.1634   $185.16   $185.15   $185.20  
  Purchase #2 $224.33   7.859%   $241.9601   $241.96   $241.95   $242.00  
  Purchase #3 $231.30   11.163%   $257.12   $257.12   $257.10   $257.10  
  Purchase #4 $230.43   12.436%   $259.0863   $259.09   $259.10   $259.10  
  Purchase #5 $225.32   9.189%   $246.0247   $246.02   $246.00   $246.00  
  Purchase #6 $31.67   5.500%   $33.4119   $33.41   $33.40   $33.40  
  Purchase #7 $49.43   5.597%   $52.1966   $52.20   $52.20   $52.20  
  7 purchase totals = $1,162.07       $1,274.9630   $1,274.96   $1,274.90   $1,275.00