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   13.187%   $273.1995   $273.20   $273.20   $273.20  
  Purchase #2 $161.80   6.663%   $172.5807   $172.58   $172.60   $172.60  
  Purchase #3 $14.69   9.560%   $16.0944   $16.09   $16.10   $16.10  
  Purchase #4 $247.46   3.381%   $255.8266   $255.83   $255.85   $255.80  
  Purchase #5 $85.94   12.571%   $96.7435   $96.74   $96.75   $96.70  
  Purchase #6 $219.80   13.763%   $250.0511   $250.05   $250.05   $250.10  
  Purchase #7 $64.50   4.788%   $67.5883   $67.59   $67.60   $67.60  
  7 purchase totals = $1,035.56       $1,132.0841   $1,132.08   $1,132.15   $1,132.10