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 $248.50   11.201%   $276.3345   $276.33   $276.35   $276.30  
  Purchase #2 $69.95   4.798%   $73.3062   $73.31   $73.30   $73.30  
  Purchase #3 $229.66   3.298%   $237.2342   $237.23   $237.25   $237.20  
  Purchase #4 $30.52   7.301%   $32.7483   $32.75   $32.75   $32.70  
  Purchase #5 $114.48   9.113%   $124.9126   $124.91   $124.90   $124.90  
  Purchase #6 $30.94   11.133%   $34.3846   $34.38   $34.40   $34.40  
  Purchase #7 $120.25   8.248%   $130.1682   $130.17   $130.15   $130.20  
  7 purchase totals = $844.30       $909.0886   $909.08   $909.10   $909.00