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 $84.26   9.793%   $92.5116   $92.51   $92.50   $92.50  
  Purchase #2 $186.91   13.395%   $211.9466   $211.95   $211.95   $211.90  
  Purchase #3 $121.70   3.421%   $125.8634   $125.86   $125.85   $125.90  
  Purchase #4 $163.67   12.161%   $183.5739   $183.57   $183.55   $183.60  
  Purchase #5 $56.32   4.738%   $58.9884   $58.99   $59.00   $59.00  
  Purchase #6 $113.81   4.255%   $118.6526   $118.65   $118.65   $118.70  
  Purchase #7 $226.79   9.511%   $248.36   $248.36   $248.35   $248.40  
  7 purchase totals = $953.46       $1,039.8965   $1,039.89   $1,039.85   $1,040.00