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 $67.33   11.128%   $74.8225   $74.82   $74.80   $74.80  
  Purchase #2 $240.41   3.141%   $247.9613   $247.96   $247.95   $248.00  
  Purchase #3 $219.65   9.841%   $241.2658   $241.27   $241.25   $241.30  
  Purchase #4 $218.94   13.434%   $248.3524   $248.35   $248.35   $248.40  
  Purchase #5 $59.66   11.793%   $66.6957   $66.70   $66.70   $66.70  
  Purchase #6 $114.72   11.543%   $127.9621   $127.96   $127.95   $128.00  
  Purchase #7 $229.87   9.164%   $250.9353   $250.94   $250.95   $250.90  
  7 purchase totals = $1,150.58       $1,257.9951   $1,258.00   $1,257.95   $1,258.10