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 $105.93   3.537%   $109.6767   $109.68   $109.70   $109.70  
  Purchase #2 $175.67   10.158%   $193.5146   $193.51   $193.50   $193.50  
  Purchase #3 $88.35   13.848%   $100.5847   $100.58   $100.60   $100.60  
  Purchase #4 $32.25   7.526%   $34.6771   $34.68   $34.70   $34.70  
  Purchase #5 $242.53   3.376%   $250.7178   $250.72   $250.70   $250.70  
  Purchase #6 $106.95   9.282%   $116.8771   $116.88   $116.90   $116.90  
  Purchase #7 $221.96   9.737%   $243.5722   $243.57   $243.55   $243.60  
  7 purchase totals = $973.64       $1,049.6202   $1,049.62   $1,049.65   $1,049.70