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 $88.48   4.654%   $92.5979   $92.60   $92.60   $92.60  
  Purchase #2 $192.39   9.326%   $210.3323   $210.33   $210.35   $210.30  
  Purchase #3 $88.33   7.593%   $95.0369   $95.04   $95.05   $95.00  
  Purchase #4 $216.67   9.847%   $238.0055   $238.01   $238.00   $238.00  
  Purchase #5 $161.33   4.665%   $168.856   $168.86   $168.85   $168.90  
  Purchase #6 $52.99   6.480%   $56.4238   $56.42   $56.40   $56.40  
  Purchase #7 $116.62   5.455%   $122.9816   $122.98   $123.00   $123.00  
  7 purchase totals = $916.81       $984.2340   $984.24   $984.25   $984.20