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 $56.85   3.866%   $59.0478   $59.05   $59.05   $59.00  
  Purchase #2 $104.81   3.521%   $108.5004   $108.50   $108.50   $108.50  
  Purchase #3 $72.39   11.485%   $80.704   $80.70   $80.70   $80.70  
  Purchase #4 $49.80   5.454%   $52.5161   $52.52   $52.50   $52.50  
  Purchase #5 $186.39   11.739%   $208.2703   $208.27   $208.25   $208.30  
  Purchase #6 $191.58   6.441%   $203.9197   $203.92   $203.90   $203.90  
  Purchase #7 $11.61   3.575%   $12.0251   $12.03   $12.05   $12.00  
  7 purchase totals = $673.43       $724.9834   $724.99   $724.95   $724.90