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 $214.88   5.804%   $227.3516   $227.35   $227.35   $227.40  
  Purchase #2 $230.81   8.330%   $250.0365   $250.04   $250.05   $250.00  
  Purchase #3 $134.49   7.635%   $144.7583   $144.76   $144.75   $144.80  
  Purchase #4 $229.61   10.351%   $253.3769   $253.38   $253.40   $253.40  
  Purchase #5 $75.59   12.607%   $85.1196   $85.12   $85.10   $85.10  
  Purchase #6 $174.88   6.529%   $186.2979   $186.30   $186.30   $186.30  
  Purchase #7 $100.89   5.774%   $106.7154   $106.72   $106.70   $106.70  
  7 purchase totals = $1,161.15       $1,253.6562   $1,253.67   $1,253.65   $1,253.70