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 $23.67   9.743%   $25.9762   $25.98   $26.00   $26.00  
  Purchase #2 $45.78   11.573%   $51.0781   $51.08   $51.10   $51.10  
  Purchase #3 $170.38   7.693%   $183.4873   $183.49   $183.50   $183.50  
  Purchase #4 $58.50   8.206%   $63.3005   $63.30   $63.30   $63.30  
  Purchase #5 $122.60   8.667%   $133.2257   $133.23   $133.25   $133.20  
  Purchase #6 $16.74   10.550%   $18.5061   $18.51   $18.50   $18.50  
  Purchase #7 $142.64   9.131%   $155.6645   $155.66   $155.65   $155.70  
  7 purchase totals = $580.31       $631.2384   $631.25   $631.30   $631.30