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 $53.94   12.332%   $60.5919   $60.59   $60.60   $60.60  
  Purchase #2 $133.64   6.418%   $142.217   $142.22   $142.20   $142.20  
  Purchase #3 $24.66   7.519%   $26.5142   $26.51   $26.50   $26.50  
  Purchase #4 $172.28   8.423%   $186.7911   $186.79   $186.80   $186.80  
  Purchase #5 $33.43   8.249%   $36.1876   $36.19   $36.20   $36.20  
  Purchase #6 $177.29   13.831%   $201.811   $201.81   $201.80   $201.80  
  Purchase #7 $223.35   11.404%   $248.8208   $248.82   $248.80   $248.80  
  7 purchase totals = $818.59       $902.9336   $902.93   $902.90   $902.90