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 $44.27   13.709%   $50.339   $50.34   $50.35   $50.30  
  Purchase #2 $168.97   8.384%   $183.1364   $183.14   $183.15   $183.10  
  Purchase #3 $216.99   3.459%   $224.4957   $224.50   $224.50   $224.50  
  Purchase #4 $179.29   11.223%   $199.4117   $199.41   $199.40   $199.40  
  Purchase #5 $52.92   6.676%   $56.4529   $56.45   $56.45   $56.50  
  Purchase #6 $179.51   9.545%   $196.6442   $196.64   $196.65   $196.60  
  Purchase #7 $110.62   12.737%   $124.7097   $124.71   $124.70   $124.70  
  7 purchase totals = $952.57       $1,035.1896   $1,035.19   $1,035.20   $1,035.10