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 $56.56   7.418%   $60.7556   $60.76   $60.75   $60.80  
  Purchase #2 $71.61   8.563%   $77.742   $77.74   $77.75   $77.70  
  Purchase #3 $210.58   11.143%   $234.0449   $234.04   $234.05   $234.00  
  Purchase #4 $80.67   10.535%   $89.1686   $89.17   $89.15   $89.20  
  Purchase #5 $8.67   6.794%   $9.259   $9.26   $9.25   $9.30  
  Purchase #6 $127.35   7.118%   $136.4148   $136.41   $136.40   $136.40  
  Purchase #7 $15.94   8.333%   $17.2683   $17.27   $17.25   $17.30  
  7 purchase totals = $571.38       $624.6532   $624.65   $624.60   $624.70