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 $65.47   7.531%   $70.4005   $70.40   $70.40   $70.40  
  Purchase #2 $236.54   4.264%   $246.6261   $246.63   $246.65   $246.60  
  Purchase #3 $202.89   5.369%   $213.7832   $213.78   $213.80   $213.80  
  Purchase #4 $34.63   3.110%   $35.707   $35.71   $35.70   $35.70  
  Purchase #5 $247.63   7.271%   $265.6352   $265.64   $265.65   $265.60  
  Purchase #6 $111.45   6.838%   $119.071   $119.07   $119.05   $119.10  
  Purchase #7 $197.56   6.823%   $211.0395   $211.04   $211.05   $211.00  
  7 purchase totals = $1,096.17       $1,162.2625   $1,162.27   $1,162.30   $1,162.20