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 $190.26   3.437%   $196.7992   $196.80   $196.80   $196.80  
  Purchase #2 $231.54   4.751%   $242.5405   $242.54   $242.55   $242.50  
  Purchase #3 $83.77   3.581%   $86.7698   $86.77   $86.75   $86.80  
  Purchase #4 $54.53   6.331%   $57.9823   $57.98   $58.00   $58.00  
  Purchase #5 $32.43   6.464%   $34.5263   $34.53   $34.55   $34.50  
  Purchase #6 $214.35   9.620%   $234.9705   $234.97   $234.95   $235.00  
  Purchase #7 $142.33   12.105%   $159.559   $159.56   $159.55   $159.60  
  7 purchase totals = $949.21       $1,013.1476   $1,013.15   $1,013.15   $1,013.20