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 $165.72   9.255%   $181.0574   $181.06   $181.05   $181.10  
  Purchase #2 $167.27   11.482%   $186.4759   $186.48   $186.50   $186.50  
  Purchase #3 $105.29   9.182%   $114.9577   $114.96   $114.95   $115.00  
  Purchase #4 $133.41   5.629%   $140.9196   $140.92   $140.90   $140.90  
  Purchase #5 $242.63   3.411%   $250.9061   $250.91   $250.90   $250.90  
  Purchase #6 $242.52   11.600%   $270.6523   $270.65   $270.65   $270.70  
  Purchase #7 $208.91   7.694%   $224.9835   $224.98   $225.00   $225.00  
  7 purchase totals = $1,265.75       $1,369.9525   $1,369.96   $1,369.95   $1,370.10