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 $103.49   11.359%   $115.2454   $115.25   $115.25   $115.20  
  Purchase #2 $186.28   4.109%   $193.9342   $193.93   $193.95   $193.90  
  Purchase #3 $128.49   7.743%   $138.439   $138.44   $138.45   $138.40  
  Purchase #4 $196.45   3.815%   $203.9446   $203.94   $203.95   $203.90  
  Purchase #5 $235.54   6.130%   $249.9786   $249.98   $250.00   $250.00  
  Purchase #6 $153.75   5.441%   $162.1155   $162.12   $162.10   $162.10  
  Purchase #7 $153.29   5.325%   $161.4527   $161.45   $161.45   $161.50  
  7 purchase totals = $1,157.29       $1,225.1100   $1,225.11   $1,225.15   $1,225.00