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 $168.73   6.555%   $179.7903   $179.79   $179.80   $179.80  
  Purchase #2 $106.35   11.604%   $118.6909   $118.69   $118.70   $118.70  
  Purchase #3 $182.28   12.230%   $204.5728   $204.57   $204.55   $204.60  
  Purchase #4 $248.82   7.331%   $267.061   $267.06   $267.05   $267.10  
  Purchase #5 $59.78   9.572%   $65.5021   $65.50   $65.50   $65.50  
  Purchase #6 $176.34   12.699%   $198.7334   $198.73   $198.75   $198.70  
  Purchase #7 $130.92   8.271%   $141.7484   $141.75   $141.75   $141.70  
  7 purchase totals = $1,073.22       $1,176.0989   $1,176.09   $1,176.10   $1,176.10