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 $237.59   10.587%   $262.7437   $262.74   $262.75   $262.70  
  Purchase #2 $40.71   12.603%   $45.8407   $45.84   $45.85   $45.80  
  Purchase #3 $27.45   11.864%   $30.7067   $30.71   $30.70   $30.70  
  Purchase #4 $214.28   9.689%   $235.0416   $235.04   $235.05   $235.00  
  Purchase #5 $85.43   12.139%   $95.8003   $95.80   $95.80   $95.80  
  Purchase #6 $105.26   8.731%   $114.4503   $114.45   $114.45   $114.50  
  Purchase #7 $92.84   7.655%   $99.9469   $99.95   $99.95   $99.90  
  7 purchase totals = $803.56       $884.5302   $884.53   $884.55   $884.40