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 $88.69   11.217%   $98.6384   $98.64   $98.65   $98.60  
  Purchase #2 $130.27   4.322%   $135.9003   $135.90   $135.90   $135.90  
  Purchase #3 $172.43   8.596%   $187.2521   $187.25   $187.25   $187.30  
  Purchase #4 $96.75   11.693%   $108.063   $108.06   $108.05   $108.10  
  Purchase #5 $97.70   7.421%   $104.9503   $104.95   $104.95   $105.00  
  Purchase #6 $230.39   8.352%   $249.6322   $249.63   $249.65   $249.60  
  Purchase #7 $129.70   6.298%   $137.8685   $137.87   $137.85   $137.90  
  7 purchase totals = $945.93       $1,022.3048   $1,022.30   $1,022.30   $1,022.40