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 $61.39   8.340%   $66.5099   $66.51   $66.50   $66.50  
  Purchase #2 $109.79   3.601%   $113.7435   $113.74   $113.75   $113.70  
  Purchase #3 $124.39   8.305%   $134.7206   $134.72   $134.70   $134.70  
  Purchase #4 $224.51   13.652%   $255.1601   $255.16   $255.15   $255.20  
  Purchase #5 $49.83   9.835%   $54.7308   $54.73   $54.75   $54.70  
  Purchase #6 $181.31   4.684%   $189.8026   $189.80   $189.80   $189.80  
  Purchase #7 $246.44   4.829%   $258.3406   $258.34   $258.35   $258.30  
  7 purchase totals = $997.66       $1,073.0081   $1,073.00   $1,073.00   $1,072.90