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 $198.95   4.196%   $207.2979   $207.30   $207.30   $207.30  
  Purchase #2 $55.58   4.292%   $57.9655   $57.97   $57.95   $58.00  
  Purchase #3 $6.60   6.165%   $7.0069   $7.01   $7.00   $7.00  
  Purchase #4 $245.57   11.508%   $273.8302   $273.83   $273.85   $273.80  
  Purchase #5 $146.35   13.566%   $166.2038   $166.20   $166.20   $166.20  
  Purchase #6 $193.37   11.618%   $215.8357   $215.84   $215.85   $215.80  
  Purchase #7 $34.26   11.106%   $38.0649   $38.06   $38.05   $38.10  
  7 purchase totals = $880.68       $966.2049   $966.21   $966.20   $966.20