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 $68.43   13.389%   $77.5921   $77.59   $77.60   $77.60  
  Purchase #2 $45.75   13.765%   $52.0475   $52.05   $52.05   $52.00  
  Purchase #3 $77.47   9.776%   $85.0435   $85.04   $85.05   $85.00  
  Purchase #4 $94.96   4.402%   $99.1401   $99.14   $99.15   $99.10  
  Purchase #5 $246.90   8.366%   $267.5557   $267.56   $267.55   $267.60  
  Purchase #6 $94.99   10.791%   $105.2404   $105.24   $105.25   $105.20  
  Purchase #7 $188.27   10.619%   $208.2624   $208.26   $208.25   $208.30  
  7 purchase totals = $816.77       $894.8817   $894.88   $894.90   $894.80