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 $204.75   10.619%   $226.4924   $226.49   $226.50   $226.50  
  Purchase #2 $92.61   5.135%   $97.3655   $97.37   $97.35   $97.40  
  Purchase #3 $98.62   8.842%   $107.34   $107.34   $107.35   $107.30  
  Purchase #4 $74.62   13.512%   $84.7027   $84.70   $84.70   $84.70  
  Purchase #5 $43.67   6.732%   $46.6099   $46.61   $46.60   $46.60  
  Purchase #6 $155.91   4.147%   $162.3756   $162.38   $162.40   $162.40  
  Purchase #7 $181.40   5.843%   $191.9992   $192.00   $192.00   $192.00  
  7 purchase totals = $851.58       $916.8853   $916.89   $916.90   $916.90