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 $241.37   11.756%   $269.7455   $269.75   $269.75   $269.70  
  Purchase #2 $85.95   11.635%   $95.9503   $95.95   $95.95   $96.00  
  Purchase #3 $62.49   13.471%   $70.908   $70.91   $70.90   $70.90  
  Purchase #4 $135.55   6.673%   $144.5953   $144.60   $144.60   $144.60  
  Purchase #5 $173.61   10.638%   $192.0786   $192.08   $192.10   $192.10  
  Purchase #6 $223.61   12.609%   $251.805   $251.81   $251.80   $251.80  
  Purchase #7 $198.46   13.347%   $224.9485   $224.95   $224.95   $224.90  
  7 purchase totals = $1,121.04       $1,250.0312   $1,250.05   $1,250.05   $1,250.00