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 $51.49   10.240%   $56.7626   $56.76   $56.75   $56.80  
  Purchase #2 $190.40   6.204%   $202.2124   $202.21   $202.20   $202.20  
  Purchase #3 $33.59   5.629%   $35.4808   $35.48   $35.50   $35.50  
  Purchase #4 $243.66   3.130%   $251.2866   $251.29   $251.30   $251.30  
  Purchase #5 $250.29   10.591%   $276.7982   $276.80   $276.80   $276.80  
  Purchase #6 $112.73   5.103%   $118.4826   $118.48   $118.50   $118.50  
  Purchase #7 $174.29   5.706%   $184.235   $184.24   $184.25   $184.20  
  7 purchase totals = $1,056.45       $1,125.2582   $1,125.26   $1,125.30   $1,125.30