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 $14.66   11.326%   $16.3204   $16.32   $16.30   $16.30  
  Purchase #2 $222.67   9.288%   $243.3516   $243.35   $243.35   $243.40  
  Purchase #3 $155.61   4.560%   $162.7058   $162.71   $162.70   $162.70  
  Purchase #4 $183.59   4.608%   $192.0498   $192.05   $192.05   $192.00  
  Purchase #5 $158.81   6.407%   $168.985   $168.99   $169.00   $169.00  
  Purchase #6 $201.60   6.869%   $215.4479   $215.45   $215.45   $215.40  
  Purchase #7 $97.77   6.291%   $103.9207   $103.92   $103.90   $103.90  
  7 purchase totals = $1,034.71       $1,102.7812   $1,102.79   $1,102.75   $1,102.70