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 $188.99   8.829%   $205.6759   $205.68   $205.70   $205.70  
  Purchase #2 $47.87   4.104%   $49.8346   $49.83   $49.85   $49.80  
  Purchase #3 $248.57   3.345%   $256.8847   $256.88   $256.90   $256.90  
  Purchase #4 $165.67   9.780%   $181.8725   $181.87   $181.85   $181.90  
  Purchase #5 $241.86   8.836%   $263.2307   $263.23   $263.25   $263.20  
  Purchase #6 $177.94   5.625%   $187.9491   $187.95   $187.95   $187.90  
  Purchase #7 $73.76   8.840%   $80.2804   $80.28   $80.30   $80.30  
  7 purchase totals = $1,144.66       $1,225.7279   $1,225.72   $1,225.80   $1,225.70