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 $194.25   6.507%   $206.8898   $206.89   $206.90   $206.90  
  Purchase #2 $196.88   6.646%   $209.9646   $209.96   $209.95   $210.00  
  Purchase #3 $137.48   8.438%   $149.0806   $149.08   $149.10   $149.10  
  Purchase #4 $81.87   12.687%   $92.2568   $92.26   $92.25   $92.30  
  Purchase #5 $24.83   5.685%   $26.2416   $26.24   $26.25   $26.20  
  Purchase #6 $143.65   7.798%   $154.8518   $154.85   $154.85   $154.90  
  Purchase #7 $60.76   3.165%   $62.6831   $62.68   $62.70   $62.70  
  7 purchase totals = $839.72       $901.9683   $901.96   $902.00   $902.10