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 $240.83   11.218%   $267.8463   $267.85   $267.85   $267.80  
  Purchase #2 $97.35   12.300%   $109.3241   $109.32   $109.30   $109.30  
  Purchase #3 $174.38   4.221%   $181.7406   $181.74   $181.75   $181.70  
  Purchase #4 $45.31   8.206%   $49.0281   $49.03   $49.05   $49.00  
  Purchase #5 $6.27   8.804%   $6.822   $6.82   $6.80   $6.80  
  Purchase #6 $152.76   6.311%   $162.4007   $162.40   $162.40   $162.40  
  Purchase #7 $68.48   6.678%   $73.0531   $73.05   $73.05   $73.10  
  7 purchase totals = $785.38       $850.2149   $850.21   $850.20   $850.10