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 $232.93   5.730%   $246.2769   $246.28   $246.30   $246.30  
  Purchase #2 $244.45   7.578%   $262.9744   $262.97   $262.95   $263.00  
  Purchase #3 $127.59   8.575%   $138.5308   $138.53   $138.55   $138.50  
  Purchase #4 $241.94   4.246%   $252.2128   $252.21   $252.20   $252.20  
  Purchase #5 $180.51   8.695%   $196.2053   $196.21   $196.20   $196.20  
  Purchase #6 $51.37   13.500%   $58.305   $58.31   $58.30   $58.30  
  Purchase #7 $100.41   4.519%   $104.9475   $104.95   $104.95   $104.90  
  7 purchase totals = $1,179.20       $1,259.4527   $1,259.46   $1,259.45   $1,259.40