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 $15.83   5.763%   $16.7423   $16.74   $16.75   $16.70  
  Purchase #2 $177.64   13.339%   $201.3354   $201.34   $201.35   $201.30  
  Purchase #3 $223.87   12.825%   $252.5813   $252.58   $252.60   $252.60  
  Purchase #4 $87.81   13.716%   $99.854   $99.85   $99.85   $99.90  
  Purchase #5 $46.73   11.821%   $52.254   $52.25   $52.25   $52.30  
  Purchase #6 $160.94   5.241%   $169.3749   $169.37   $169.35   $169.40  
  Purchase #7 $202.25   6.569%   $215.5358   $215.54   $215.55   $215.50  
  7 purchase totals = $915.07       $1,007.6777   $1,007.67   $1,007.70   $1,007.70