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 $57.90   6.146%   $61.4585   $61.46   $61.45   $61.50  
  Purchase #2 $108.60   5.713%   $114.8043   $114.80   $114.80   $114.80  
  Purchase #3 $55.48   13.822%   $63.1484   $63.15   $63.15   $63.10  
  Purchase #4 $132.55   6.311%   $140.9152   $140.92   $140.90   $140.90  
  Purchase #5 $207.72   7.870%   $224.0676   $224.07   $224.05   $224.10  
  Purchase #6 $239.72   4.766%   $251.1451   $251.15   $251.15   $251.10  
  Purchase #7 $194.90   12.816%   $219.8784   $219.88   $219.90   $219.90  
  7 purchase totals = $996.87       $1,075.4175   $1,075.43   $1,075.40   $1,075.40