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 $87.74   9.510%   $96.0841   $96.08   $96.10   $96.10  
  Purchase #2 $133.85   11.107%   $148.7167   $148.72   $148.70   $148.70  
  Purchase #3 $120.60   4.771%   $126.3538   $126.35   $126.35   $126.40  
  Purchase #4 $93.95   4.601%   $98.2726   $98.27   $98.25   $98.30  
  Purchase #5 $207.48   11.137%   $230.587   $230.59   $230.60   $230.60  
  Purchase #6 $51.61   4.495%   $53.9299   $53.93   $53.95   $53.90  
  Purchase #7 $18.66   4.461%   $19.4924   $19.49   $19.50   $19.50  
  7 purchase totals = $713.89       $773.4365   $773.43   $773.45   $773.50