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 $94.66   10.671%   $104.7612   $104.76   $104.75   $104.80  
  Purchase #2 $70.64   9.364%   $77.2547   $77.25   $77.25   $77.30  
  Purchase #3 $43.66   8.143%   $47.2152   $47.22   $47.20   $47.20  
  Purchase #4 $237.45   11.129%   $263.8758   $263.88   $263.90   $263.90  
  Purchase #5 $10.64   11.536%   $11.8674   $11.87   $11.85   $11.90  
  Purchase #6 $180.45   12.540%   $203.0784   $203.08   $203.10   $203.10  
  Purchase #7 $121.40   10.376%   $133.9965   $134.00   $134.00   $134.00  
  7 purchase totals = $758.90       $842.0492   $842.06   $842.05   $842.20