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 $105.67   8.806%   $114.9753   $114.98   $115.00   $115.00  
  Purchase #2 $27.67   5.444%   $29.1764   $29.18   $29.20   $29.20  
  Purchase #3 $12.96   11.201%   $14.4116   $14.41   $14.40   $14.40  
  Purchase #4 $245.75   11.270%   $273.446   $273.45   $273.45   $273.40  
  Purchase #5 $142.59   4.226%   $148.6159   $148.62   $148.60   $148.60  
  Purchase #6 $235.73   7.283%   $252.8982   $252.90   $252.90   $252.90  
  Purchase #7 $166.98   10.333%   $184.234   $184.23   $184.25   $184.20  
  7 purchase totals = $937.35       $1,017.7574   $1,017.77   $1,017.80   $1,017.70