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 $107.96   3.203%   $111.418   $111.42   $111.40   $111.40  
  Purchase #2 $194.25   13.218%   $219.926   $219.93   $219.95   $219.90  
  Purchase #3 $225.42   11.668%   $251.722   $251.72   $251.70   $251.70  
  Purchase #4 $106.26   7.281%   $113.9968   $114.00   $114.00   $114.00  
  Purchase #5 $58.44   5.551%   $61.684   $61.68   $61.70   $61.70  
  Purchase #6 $197.84   8.436%   $214.5298   $214.53   $214.55   $214.50  
  Purchase #7 $19.42   5.730%   $20.5328   $20.53   $20.55   $20.50  
  7 purchase totals = $909.59       $993.8094   $993.81   $993.85   $993.70