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 $61.61   6.857%   $65.8346   $65.83   $65.85   $65.80  
  Purchase #2 $233.90   10.672%   $258.8618   $258.86   $258.85   $258.90  
  Purchase #3 $146.94   11.468%   $163.7911   $163.79   $163.80   $163.80  
  Purchase #4 $199.28   3.551%   $206.3564   $206.36   $206.35   $206.40  
  Purchase #5 $33.67   8.510%   $36.5353   $36.54   $36.55   $36.50  
  Purchase #6 $83.80   9.248%   $91.5498   $91.55   $91.55   $91.50  
  Purchase #7 $211.55   4.246%   $220.5324   $220.53   $220.55   $220.50  
  7 purchase totals = $970.75       $1,043.4614   $1,043.46   $1,043.50   $1,043.40