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 $58.48   8.634%   $63.5292   $63.53   $63.55   $63.50  
  Purchase #2 $94.32   7.706%   $101.5883   $101.59   $101.60   $101.60  
  Purchase #3 $211.63   6.472%   $225.3267   $225.33   $225.35   $225.30  
  Purchase #4 $14.99   9.552%   $16.4218   $16.42   $16.40   $16.40  
  Purchase #5 $240.31   10.613%   $265.8141   $265.81   $265.80   $265.80  
  Purchase #6 $158.64   13.129%   $179.4678   $179.47   $179.45   $179.50  
  Purchase #7 $86.35   6.649%   $92.0914   $92.09   $92.10   $92.10  
  7 purchase totals = $864.72       $944.2393   $944.24   $944.25   $944.20