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 $239.99   11.390%   $267.3249   $267.32   $267.30   $267.30  
  Purchase #2 $228.39   10.337%   $251.9987   $252.00   $252.00   $252.00  
  Purchase #3 $90.85   8.758%   $98.8066   $98.81   $98.80   $98.80  
  Purchase #4 $41.86   3.166%   $43.1853   $43.19   $43.20   $43.20  
  Purchase #5 $22.61   12.448%   $25.4245   $25.42   $25.40   $25.40  
  Purchase #6 $202.26   11.440%   $225.3985   $225.40   $225.40   $225.40  
  Purchase #7 $121.52   13.757%   $138.2375   $138.24   $138.25   $138.20  
  7 purchase totals = $947.48       $1,050.3760   $1,050.38   $1,050.35   $1,050.30