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 $189.51   8.627%   $205.859   $205.86   $205.85   $205.90  
  Purchase #2 $61.42   3.408%   $63.5132   $63.51   $63.50   $63.50  
  Purchase #3 $51.40   6.783%   $54.8865   $54.89   $54.90   $54.90  
  Purchase #4 $75.41   7.257%   $80.8825   $80.88   $80.90   $80.90  
  Purchase #5 $119.56   3.827%   $124.1356   $124.14   $124.15   $124.10  
  Purchase #6 $86.65   13.374%   $98.2386   $98.24   $98.25   $98.20  
  Purchase #7 $94.84   12.760%   $106.9416   $106.94   $106.95   $106.90  
  7 purchase totals = $678.79       $734.4570   $734.46   $734.50   $734.40