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 $55.50   13.810%   $63.1646   $63.16   $63.15   $63.20  
  Purchase #2 $211.86   8.578%   $230.0334   $230.03   $230.05   $230.00  
  Purchase #3 $195.96   6.590%   $208.8738   $208.87   $208.85   $208.90  
  Purchase #4 $232.92   9.397%   $254.8075   $254.81   $254.80   $254.80  
  Purchase #5 $9.88   4.150%   $10.29   $10.29   $10.30   $10.30  
  Purchase #6 $165.87   3.581%   $171.8098   $171.81   $171.80   $171.80  
  Purchase #7 $14.59   4.775%   $15.2867   $15.29   $15.30   $15.30  
  7 purchase totals = $886.58       $954.2658   $954.26   $954.25   $954.30