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 $136.56   4.734%   $143.0248   $143.02   $143.00   $143.00  
  Purchase #2 $101.93   4.243%   $106.2549   $106.25   $106.25   $106.30  
  Purchase #3 $156.80   4.564%   $163.9564   $163.96   $163.95   $164.00  
  Purchase #4 $106.70   4.797%   $111.8184   $111.82   $111.80   $111.80  
  Purchase #5 $60.57   6.533%   $64.527   $64.53   $64.55   $64.50  
  Purchase #6 $163.97   13.458%   $186.0371   $186.04   $186.05   $186.00  
  Purchase #7 $149.42   3.495%   $154.6422   $154.64   $154.65   $154.60  
  7 purchase totals = $875.95       $930.2608   $930.26   $930.25   $930.20