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 $241.79   5.262%   $254.513   $254.51   $254.50   $254.50  
  Purchase #2 $47.79   6.654%   $50.9699   $50.97   $50.95   $51.00  
  Purchase #3 $103.39   10.580%   $114.3287   $114.33   $114.35   $114.30  
  Purchase #4 $157.28   10.169%   $173.2738   $173.27   $173.25   $173.30  
  Purchase #5 $21.84   5.259%   $22.9886   $22.99   $23.00   $23.00  
  Purchase #6 $240.88   4.501%   $251.722   $251.72   $251.70   $251.70  
  Purchase #7 $195.62   7.241%   $209.7848   $209.78   $209.80   $209.80  
  7 purchase totals = $1,008.59       $1,077.5808   $1,077.57   $1,077.55   $1,077.60