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 $62.78   12.359%   $70.539   $70.54   $70.55   $70.50  
  Purchase #2 $50.52   9.576%   $55.3578   $55.36   $55.35   $55.40  
  Purchase #3 $127.67   10.809%   $141.4699   $141.47   $141.45   $141.50  
  Purchase #4 $72.75   13.780%   $82.775   $82.78   $82.80   $82.80  
  Purchase #5 $75.91   8.163%   $82.1065   $82.11   $82.10   $82.10  
  Purchase #6 $23.69   12.399%   $26.6273   $26.63   $26.65   $26.60  
  Purchase #7 $69.72   8.824%   $75.8721   $75.87   $75.85   $75.90  
  7 purchase totals = $483.04       $534.7476   $534.76   $534.75   $534.80