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 $120.56   3.134%   $124.3384   $124.34   $124.35   $124.30  
  Purchase #2 $221.66   5.515%   $233.8845   $233.88   $233.90   $233.90  
  Purchase #3 $61.90   9.444%   $67.7458   $67.75   $67.75   $67.70  
  Purchase #4 $119.92   3.463%   $124.0728   $124.07   $124.05   $124.10  
  Purchase #5 $93.45   3.318%   $96.5507   $96.55   $96.55   $96.60  
  Purchase #6 $220.94   8.574%   $239.8834   $239.88   $239.90   $239.90  
  Purchase #7 $156.93   10.208%   $172.9494   $172.95   $172.95   $172.90  
  7 purchase totals = $995.36       $1,059.4250   $1,059.42   $1,059.45   $1,059.40