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 $228.51   9.450%   $250.1042   $250.10   $250.10   $250.10  
  Purchase #2 $228.27   9.214%   $249.3028   $249.30   $249.30   $249.30  
  Purchase #3 $58.31   3.769%   $60.5077   $60.51   $60.50   $60.50  
  Purchase #4 $170.35   4.452%   $177.934   $177.93   $177.95   $177.90  
  Purchase #5 $209.51   12.612%   $235.9334   $235.93   $235.95   $235.90  
  Purchase #6 $17.97   13.128%   $20.3291   $20.33   $20.35   $20.30  
  Purchase #7 $6.65   12.178%   $7.4598   $7.46   $7.45   $7.50  
  7 purchase totals = $919.57       $1,001.5710   $1,001.56   $1,001.60   $1,001.50