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 $57.37   7.591%   $61.725   $61.73   $61.75   $61.70  
  Purchase #2 $35.44   6.864%   $37.8726   $37.87   $37.85   $37.90  
  Purchase #3 $66.46   12.590%   $74.8273   $74.83   $74.85   $74.80  
  Purchase #4 $222.84   6.371%   $237.0371   $237.04   $237.05   $237.00  
  Purchase #5 $66.92   3.752%   $69.4308   $69.43   $69.45   $69.40  
  Purchase #6 $36.40   3.180%   $37.5575   $37.56   $37.55   $37.60  
  Purchase #7 $83.65   4.698%   $87.5799   $87.58   $87.60   $87.60  
  7 purchase totals = $569.08       $606.0302   $606.04   $606.10   $606.00