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 $61.42   11.586%   $68.5361   $68.54   $68.55   $68.50  
  Purchase #2 $231.92   3.769%   $240.6611   $240.66   $240.65   $240.70  
  Purchase #3 $199.81   7.824%   $215.4431   $215.44   $215.45   $215.40  
  Purchase #4 $54.81   6.448%   $58.3441   $58.34   $58.35   $58.30  
  Purchase #5 $118.53   12.847%   $133.7575   $133.76   $133.75   $133.80  
  Purchase #6 $237.82   4.504%   $248.5314   $248.53   $248.55   $248.50  
  Purchase #7 $56.52   7.826%   $60.9433   $60.94   $60.95   $60.90  
  7 purchase totals = $960.83       $1,026.2166   $1,026.21   $1,026.25   $1,026.10