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 $84.59   9.234%   $92.401   $92.40   $92.40   $92.40  
  Purchase #2 $44.95   5.723%   $47.5225   $47.52   $47.50   $47.50  
  Purchase #3 $70.48   7.744%   $75.938   $75.94   $75.95   $75.90  
  Purchase #4 $50.82   3.383%   $52.5392   $52.54   $52.55   $52.50  
  Purchase #5 $91.27   3.163%   $94.1569   $94.16   $94.15   $94.20  
  Purchase #6 $153.85   4.128%   $160.2009   $160.20   $160.20   $160.20  
  Purchase #7 $223.61   4.766%   $234.2673   $234.27   $234.25   $234.30  
  7 purchase totals = $719.57       $757.0258   $757.03   $757.00   $757.00