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 $230.51   11.631%   $257.3206   $257.32   $257.30   $257.30  
  Purchase #2 $38.53   13.396%   $43.6915   $43.69   $43.70   $43.70  
  Purchase #3 $225.59   12.622%   $254.064   $254.06   $254.05   $254.10  
  Purchase #4 $232.47   10.265%   $256.333   $256.33   $256.35   $256.30  
  Purchase #5 $113.37   10.589%   $125.3747   $125.37   $125.35   $125.40  
  Purchase #6 $25.91   3.680%   $26.8635   $26.86   $26.85   $26.90  
  Purchase #7 $81.37   12.638%   $91.6535   $91.65   $91.65   $91.70  
  7 purchase totals = $947.75       $1,055.3008   $1,055.28   $1,055.25   $1,055.40