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 $41.32   8.410%   $44.795   $44.80   $44.80   $44.80  
  Purchase #2 $56.64   8.866%   $61.6617   $61.66   $61.65   $61.70  
  Purchase #3 $47.72   12.721%   $53.7905   $53.79   $53.80   $53.80  
  Purchase #4 $198.94   5.848%   $210.574   $210.57   $210.55   $210.60  
  Purchase #5 $110.96   12.491%   $124.82   $124.82   $124.80   $124.80  
  Purchase #6 $47.96   6.762%   $51.2031   $51.20   $51.20   $51.20  
  Purchase #7 $154.56   4.122%   $160.931   $160.93   $160.95   $160.90  
  7 purchase totals = $658.10       $707.7753   $707.77   $707.75   $707.80