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 $189.70   9.636%   $207.9795   $207.98   $208.00   $208.00  
  Purchase #2 $56.41   10.135%   $62.1272   $62.13   $62.15   $62.10  
  Purchase #3 $178.49   10.474%   $197.185   $197.19   $197.20   $197.20  
  Purchase #4 $20.87   6.668%   $22.2616   $22.26   $22.25   $22.30  
  Purchase #5 $168.31   13.367%   $190.808   $190.81   $190.80   $190.80  
  Purchase #6 $56.30   3.134%   $58.0644   $58.06   $58.05   $58.10  
  Purchase #7 $16.47   3.271%   $17.0087   $17.01   $17.00   $17.00  
  7 purchase totals = $686.55       $755.4344   $755.44   $755.45   $755.50