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 $208.33   6.543%   $221.961   $221.96   $221.95   $222.00  
  Purchase #2 $175.35   8.777%   $190.7405   $190.74   $190.75   $190.70  
  Purchase #3 $41.61   4.659%   $43.5486   $43.55   $43.55   $43.50  
  Purchase #4 $183.61   7.470%   $197.3257   $197.33   $197.35   $197.30  
  Purchase #5 $239.26   8.696%   $260.066   $260.07   $260.05   $260.10  
  Purchase #6 $111.74   9.607%   $122.4749   $122.47   $122.45   $122.50  
  Purchase #7 $8.52   13.798%   $9.6956   $9.70   $9.70   $9.70  
  7 purchase totals = $968.42       $1,045.8123   $1,045.82   $1,045.80   $1,045.80