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 $9.58   3.300%   $9.8961   $9.90   $9.90   $9.90  
  Purchase #2 $121.64   4.349%   $126.9301   $126.93   $126.95   $126.90  
  Purchase #3 $214.27   10.709%   $237.2162   $237.22   $237.20   $237.20  
  Purchase #4 $109.99   12.756%   $124.0203   $124.02   $124.00   $124.00  
  Purchase #5 $21.64   11.227%   $24.0695   $24.07   $24.05   $24.10  
  Purchase #6 $74.71   8.264%   $80.884   $80.88   $80.90   $80.90  
  Purchase #7 $225.60   8.326%   $244.3835   $244.38   $244.40   $244.40  
  7 purchase totals = $777.43       $847.3997   $847.40   $847.40   $847.40