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 $244.59   9.452%   $267.7086   $267.71   $267.70   $267.70  
  Purchase #2 $98.80   13.409%   $112.0481   $112.05   $112.05   $112.00  
  Purchase #3 $172.59   13.807%   $196.4195   $196.42   $196.40   $196.40  
  Purchase #4 $109.30   10.331%   $120.5918   $120.59   $120.60   $120.60  
  Purchase #5 $247.98   10.423%   $273.827   $273.83   $273.85   $273.80  
  Purchase #6 $179.87   10.346%   $198.4794   $198.48   $198.50   $198.50  
  Purchase #7 $25.34   5.122%   $26.6379   $26.64   $26.65   $26.60  
  7 purchase totals = $1,078.47       $1,195.7123   $1,195.72   $1,195.75   $1,195.60