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 $208.58   13.151%   $236.0104   $236.01   $236.00   $236.00  
  Purchase #2 $104.97   3.705%   $108.8591   $108.86   $108.85   $108.90  
  Purchase #3 $98.84   4.272%   $103.0624   $103.06   $103.05   $103.10  
  Purchase #4 $120.84   3.243%   $124.7588   $124.76   $124.75   $124.80  
  Purchase #5 $68.95   12.818%   $77.788   $77.79   $77.80   $77.80  
  Purchase #6 $122.32   6.737%   $130.5607   $130.56   $130.55   $130.60  
  Purchase #7 $142.99   4.224%   $149.0299   $149.03   $149.05   $149.00  
  7 purchase totals = $867.49       $930.0693   $930.07   $930.05   $930.20