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 $39.83   8.475%   $43.2056   $43.21   $43.20   $43.20  
  Purchase #2 $203.75   10.236%   $224.6059   $224.61   $224.60   $224.60  
  Purchase #3 $75.52   4.809%   $79.1518   $79.15   $79.15   $79.20  
  Purchase #4 $21.62   7.628%   $23.2692   $23.27   $23.25   $23.30  
  Purchase #5 $197.54   11.871%   $220.99   $220.99   $221.00   $221.00  
  Purchase #6 $158.49   4.192%   $165.1339   $165.13   $165.15   $165.10  
  Purchase #7 $136.94   8.705%   $148.8606   $148.86   $148.85   $148.90  
  7 purchase totals = $833.69       $905.2170   $905.22   $905.20   $905.30