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 $56.56   12.843%   $63.824   $63.82   $63.80   $63.80  
  Purchase #2 $29.49   13.658%   $33.5177   $33.52   $33.50   $33.50  
  Purchase #3 $131.88   7.675%   $142.0018   $142.00   $142.00   $142.00  
  Purchase #4 $5.69   5.705%   $6.0146   $6.01   $6.00   $6.00  
  Purchase #5 $227.61   7.299%   $244.2233   $244.22   $244.20   $244.20  
  Purchase #6 $246.49   3.512%   $255.1467   $255.15   $255.15   $255.10  
  Purchase #7 $48.33   8.318%   $52.3501   $52.35   $52.35   $52.40  
  7 purchase totals = $746.05       $797.0782   $797.07   $797.00   $797.00