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 $211.89   11.126%   $235.4649   $235.46   $235.45   $235.50  
  Purchase #2 $202.25   6.626%   $215.6511   $215.65   $215.65   $215.70  
  Purchase #3 $242.86   3.749%   $251.9648   $251.96   $251.95   $252.00  
  Purchase #4 $63.59   11.279%   $70.7623   $70.76   $70.75   $70.80  
  Purchase #5 $113.88   12.534%   $128.1537   $128.15   $128.15   $128.20  
  Purchase #6 $241.65   9.583%   $264.8073   $264.81   $264.80   $264.80  
  Purchase #7 $237.93   4.475%   $248.5774   $248.58   $248.60   $248.60  
  7 purchase totals = $1,314.05       $1,415.3815   $1,415.37   $1,415.35   $1,415.60