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 $86.53   10.827%   $95.8986   $95.90   $95.90   $95.90  
  Purchase #2 $220.63   8.843%   $240.1403   $240.14   $240.15   $240.10  
  Purchase #3 $18.58   8.838%   $20.2221   $20.22   $20.20   $20.20  
  Purchase #4 $66.53   11.470%   $74.161   $74.16   $74.15   $74.20  
  Purchase #5 $131.70   7.285%   $141.2943   $141.29   $141.30   $141.30  
  Purchase #6 $22.46   10.153%   $24.7404   $24.74   $24.75   $24.70  
  Purchase #7 $153.31   5.799%   $162.2004   $162.20   $162.20   $162.20  
  7 purchase totals = $699.74       $758.6571   $758.65   $758.65   $758.60