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 $96.59   6.870%   $103.2257   $103.23   $103.25   $103.20  
  Purchase #2 $63.85   6.312%   $67.8802   $67.88   $67.90   $67.90  
  Purchase #3 $169.52   7.382%   $182.034   $182.03   $182.05   $182.00  
  Purchase #4 $158.94   12.156%   $178.2607   $178.26   $178.25   $178.30  
  Purchase #5 $216.67   8.593%   $235.2885   $235.29   $235.30   $235.30  
  Purchase #6 $250.84   12.823%   $283.0052   $283.01   $283.00   $283.00  
  Purchase #7 $218.91   8.626%   $237.7932   $237.79   $237.80   $237.80  
  7 purchase totals = $1,175.32       $1,287.4875   $1,287.49   $1,287.55   $1,287.50