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 $226.87   8.273%   $245.639   $245.64   $245.65   $245.60  
  Purchase #2 $151.29   8.237%   $163.7518   $163.75   $163.75   $163.80  
  Purchase #3 $35.70   12.300%   $40.0911   $40.09   $40.10   $40.10  
  Purchase #4 $155.47   11.190%   $172.8671   $172.87   $172.85   $172.90  
  Purchase #5 $114.65   4.109%   $119.361   $119.36   $119.35   $119.40  
  Purchase #6 $207.83   4.525%   $217.2343   $217.23   $217.25   $217.20  
  Purchase #7 $62.97   11.751%   $70.3696   $70.37   $70.35   $70.40  
  7 purchase totals = $954.78       $1,029.3139   $1,029.31   $1,029.30   $1,029.40