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 $236.81   13.736%   $269.3382   $269.34   $269.35   $269.30  
  Purchase #2 $82.99   7.397%   $89.1288   $89.13   $89.15   $89.10  
  Purchase #3 $202.85   11.671%   $226.5246   $226.52   $226.50   $226.50  
  Purchase #4 $230.52   12.468%   $259.2612   $259.26   $259.25   $259.30  
  Purchase #5 $135.29   11.720%   $151.146   $151.15   $151.15   $151.10  
  Purchase #6 $184.55   5.193%   $194.1337   $194.13   $194.15   $194.10  
  Purchase #7 $169.81   3.233%   $175.3   $175.30   $175.30   $175.30  
  7 purchase totals = $1,242.82       $1,364.8325   $1,364.83   $1,364.85   $1,364.70