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 $66.31   5.243%   $69.7866   $69.79   $69.80   $69.80  
  Purchase #2 $235.84   5.553%   $248.9362   $248.94   $248.95   $248.90  
  Purchase #3 $229.60   8.734%   $249.6533   $249.65   $249.65   $249.70  
  Purchase #4 $180.71   6.197%   $191.9086   $191.91   $191.90   $191.90  
  Purchase #5 $153.36   11.401%   $170.8446   $170.84   $170.85   $170.80  
  Purchase #6 $48.95   3.337%   $50.5835   $50.58   $50.60   $50.60  
  Purchase #7 $237.91   13.859%   $270.8819   $270.88   $270.90   $270.90  
  7 purchase totals = $1,152.68       $1,252.5947   $1,252.59   $1,252.65   $1,252.60