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 $54.38   10.225%   $59.9404   $59.94   $59.95   $59.90  
  Purchase #2 $238.49   12.279%   $267.7742   $267.77   $267.75   $267.80  
  Purchase #3 $154.88   5.702%   $163.7113   $163.71   $163.70   $163.70  
  Purchase #4 $116.87   3.818%   $121.3321   $121.33   $121.35   $121.30  
  Purchase #5 $113.70   10.509%   $125.6487   $125.65   $125.65   $125.60  
  Purchase #6 $114.62   6.481%   $122.0485   $122.05   $122.05   $122.00  
  Purchase #7 $131.88   6.287%   $140.1713   $140.17   $140.15   $140.20  
  7 purchase totals = $924.82       $1,000.6265   $1,000.62   $1,000.60   $1,000.50