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 $103.99   8.859%   $113.2025   $113.20   $113.20   $113.20  
  Purchase #2 $225.76   11.205%   $251.0564   $251.06   $251.05   $251.10  
  Purchase #3 $48.93   12.533%   $55.0624   $55.06   $55.05   $55.10  
  Purchase #4 $165.42   11.395%   $184.2696   $184.27   $184.25   $184.30  
  Purchase #5 $169.92   9.747%   $186.4821   $186.48   $186.50   $186.50  
  Purchase #6 $57.88   8.202%   $62.6273   $62.63   $62.65   $62.60  
  Purchase #7 $49.53   13.431%   $56.1824   $56.18   $56.20   $56.20  
  7 purchase totals = $821.43       $908.8827   $908.88   $908.90   $909.00