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 $38.89   7.530%   $41.8184   $41.82   $41.80   $41.80  
  Purchase #2 $226.81   6.347%   $241.2056   $241.21   $241.20   $241.20  
  Purchase #3 $162.36   4.832%   $170.2052   $170.21   $170.20   $170.20  
  Purchase #4 $75.94   13.506%   $86.1965   $86.20   $86.20   $86.20  
  Purchase #5 $114.52   5.206%   $120.4819   $120.48   $120.50   $120.50  
  Purchase #6 $57.51   4.868%   $60.3096   $60.31   $60.30   $60.30  
  Purchase #7 $24.76   6.183%   $26.2909   $26.29   $26.30   $26.30  
  7 purchase totals = $700.79       $746.5081   $746.52   $746.50   $746.50