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 $200.87   12.635%   $226.2499   $226.25   $226.25   $226.20  
  Purchase #2 $142.34   11.744%   $159.0564   $159.06   $159.05   $159.10  
  Purchase #3 $161.72   10.487%   $178.6796   $178.68   $178.70   $178.70  
  Purchase #4 $237.77   5.594%   $251.0709   $251.07   $251.05   $251.10  
  Purchase #5 $250.63   13.792%   $285.1969   $285.20   $285.20   $285.20  
  Purchase #6 $95.63   11.524%   $106.6504   $106.65   $106.65   $106.70  
  Purchase #7 $55.42   5.737%   $58.5994   $58.60   $58.60   $58.60  
  7 purchase totals = $1,144.38       $1,265.5035   $1,265.51   $1,265.50   $1,265.60