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 $214.33   13.833%   $243.9783   $243.98   $244.00   $244.00  
  Purchase #2 $24.45   8.220%   $26.4598   $26.46   $26.45   $26.50  
  Purchase #3 $72.44   9.474%   $79.303   $79.30   $79.30   $79.30  
  Purchase #4 $208.87   11.487%   $232.8629   $232.86   $232.85   $232.90  
  Purchase #5 $42.65   7.621%   $45.9004   $45.90   $45.90   $45.90  
  Purchase #6 $79.25   5.108%   $83.2981   $83.30   $83.30   $83.30  
  Purchase #7 $107.37   11.815%   $120.0558   $120.06   $120.05   $120.10  
  7 purchase totals = $749.36       $831.8583   $831.86   $831.85   $832.00