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 $50.62   10.346%   $55.8571   $55.86   $55.85   $55.90  
  Purchase #2 $175.37   6.658%   $187.0461   $187.05   $187.05   $187.00  
  Purchase #3 $41.62   10.630%   $46.0442   $46.04   $46.05   $46.00  
  Purchase #4 $186.89   13.313%   $211.7707   $211.77   $211.75   $211.80  
  Purchase #5 $250.46   12.449%   $281.6398   $281.64   $281.65   $281.60  
  Purchase #6 $123.83   8.131%   $133.8986   $133.90   $133.90   $133.90  
  Purchase #7 $117.77   12.129%   $132.0543   $132.05   $132.05   $132.10  
  7 purchase totals = $946.56       $1,048.3108   $1,048.31   $1,048.30   $1,048.30