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 $45.83   11.112%   $50.9226   $50.92   $50.90   $50.90  
  Purchase #2 $214.91   5.667%   $227.0889   $227.09   $227.10   $227.10  
  Purchase #3 $163.51   9.729%   $179.4179   $179.42   $179.40   $179.40  
  Purchase #4 $240.37   5.247%   $252.9822   $252.98   $253.00   $253.00  
  Purchase #5 $9.30   6.828%   $9.935   $9.94   $9.95   $9.90  
  Purchase #6 $127.91   11.536%   $142.6657   $142.67   $142.65   $142.70  
  Purchase #7 $145.56   5.738%   $153.9122   $153.91   $153.90   $153.90  
  7 purchase totals = $947.39       $1,016.9245   $1,016.93   $1,016.90   $1,016.90