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 $69.88   9.646%   $76.6206   $76.62   $76.60   $76.60  
  Purchase #2 $218.48   6.613%   $232.9281   $232.93   $232.95   $232.90  
  Purchase #3 $34.33   12.344%   $38.5677   $38.57   $38.55   $38.60  
  Purchase #4 $226.78   13.698%   $257.8443   $257.84   $257.85   $257.80  
  Purchase #5 $120.74   3.861%   $125.4018   $125.40   $125.40   $125.40  
  Purchase #6 $107.28   10.554%   $118.6023   $118.60   $118.60   $118.60  
  Purchase #7 $236.58   12.319%   $265.7243   $265.72   $265.70   $265.70  
  7 purchase totals = $1,014.07       $1,115.6891   $1,115.68   $1,115.65   $1,115.60