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 $52.59   10.207%   $57.9579   $57.96   $57.95   $58.00  
  Purchase #2 $33.60   13.834%   $38.2482   $38.25   $38.25   $38.20  
  Purchase #3 $212.36   3.754%   $220.332   $220.33   $220.35   $220.30  
  Purchase #4 $22.52   13.102%   $25.4706   $25.47   $25.45   $25.50  
  Purchase #5 $124.96   4.509%   $130.5944   $130.59   $130.60   $130.60  
  Purchase #6 $10.25   10.553%   $11.3317   $11.33   $11.35   $11.30  
  Purchase #7 $91.68   4.679%   $95.9697   $95.97   $95.95   $96.00  
  7 purchase totals = $547.96       $579.9045   $579.90   $579.90   $579.90