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 $93.48   3.597%   $96.8425   $96.84   $96.85   $96.80  
  Purchase #2 $139.48   12.206%   $156.5049   $156.50   $156.50   $156.50  
  Purchase #3 $135.30   5.188%   $142.3194   $142.32   $142.30   $142.30  
  Purchase #4 $69.39   6.523%   $73.9163   $73.92   $73.90   $73.90  
  Purchase #5 $170.61   13.122%   $192.9974   $193.00   $193.00   $193.00  
  Purchase #6 $57.50   5.298%   $60.5464   $60.55   $60.55   $60.50  
  Purchase #7 $51.43   9.293%   $56.2094   $56.21   $56.20   $56.20  
  7 purchase totals = $717.19       $779.3363   $779.34   $779.30   $779.20