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 $50.56   9.178%   $55.2004   $55.20   $55.20   $55.20  
  Purchase #2 $85.48   11.199%   $95.0529   $95.05   $95.05   $95.10  
  Purchase #3 $105.37   12.692%   $118.7436   $118.74   $118.75   $118.70  
  Purchase #4 $61.70   5.296%   $64.9676   $64.97   $64.95   $65.00  
  Purchase #5 $250.42   10.539%   $276.8118   $276.81   $276.80   $276.80  
  Purchase #6 $198.30   11.138%   $220.3867   $220.39   $220.40   $220.40  
  Purchase #7 $181.46   3.827%   $188.4045   $188.40   $188.40   $188.40  
  7 purchase totals = $933.29       $1,019.5675   $1,019.56   $1,019.55   $1,019.60