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 $119.85   12.330%   $134.6275   $134.63   $134.65   $134.60  
  Purchase #2 $212.71   13.311%   $241.0238   $241.02   $241.00   $241.00  
  Purchase #3 $215.84   6.746%   $230.4006   $230.40   $230.40   $230.40  
  Purchase #4 $103.26   8.164%   $111.6901   $111.69   $111.70   $111.70  
  Purchase #5 $161.73   7.535%   $173.9164   $173.92   $173.90   $173.90  
  Purchase #6 $204.95   11.830%   $229.1956   $229.20   $229.20   $229.20  
  Purchase #7 $227.86   6.706%   $243.1403   $243.14   $243.15   $243.10  
  7 purchase totals = $1,246.20       $1,363.9943   $1,364.00   $1,364.00   $1,363.90