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 $208.77   6.357%   $222.0415   $222.04   $222.05   $222.00  
  Purchase #2 $165.26   7.330%   $177.3736   $177.37   $177.35   $177.40  
  Purchase #3 $62.55   12.718%   $70.5051   $70.51   $70.50   $70.50  
  Purchase #4 $133.71   12.380%   $150.2633   $150.26   $150.25   $150.30  
  Purchase #5 $151.28   6.587%   $161.2448   $161.24   $161.25   $161.20  
  Purchase #6 $87.56   11.204%   $97.3702   $97.37   $97.35   $97.40  
  Purchase #7 $86.25   5.192%   $90.7281   $90.73   $90.75   $90.70  
  7 purchase totals = $895.38       $969.5266   $969.52   $969.50   $969.50