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 $222.76   9.234%   $243.3297   $243.33   $243.35   $243.30  
  Purchase #2 $142.67   8.252%   $154.4431   $154.44   $154.45   $154.40  
  Purchase #3 $138.47   13.322%   $156.917   $156.92   $156.90   $156.90  
  Purchase #4 $167.72   10.536%   $185.391   $185.39   $185.40   $185.40  
  Purchase #5 $223.78   13.810%   $254.684   $254.68   $254.70   $254.70  
  Purchase #6 $238.67   5.431%   $251.6322   $251.63   $251.65   $251.60  
  Purchase #7 $222.72   13.271%   $252.2772   $252.28   $252.30   $252.30  
  7 purchase totals = $1,356.79       $1,498.6742   $1,498.67   $1,498.75   $1,498.60