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 $40.65   7.868%   $43.8483   $43.85   $43.85   $43.80  
  Purchase #2 $101.26   5.531%   $106.8607   $106.86   $106.85   $106.90  
  Purchase #3 $147.58   3.591%   $152.8796   $152.88   $152.90   $152.90  
  Purchase #4 $243.69   12.684%   $274.5996   $274.60   $274.60   $274.60  
  Purchase #5 $37.88   8.874%   $41.2415   $41.24   $41.25   $41.20  
  Purchase #6 $135.45   13.842%   $154.199   $154.20   $154.20   $154.20  
  Purchase #7 $161.57   10.327%   $178.2553   $178.26   $178.25   $178.30  
  7 purchase totals = $868.08       $951.8840   $951.89   $951.90   $951.90