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 $31.45   10.202%   $34.6585   $34.66   $34.65   $34.70  
  Purchase #2 $231.50   13.602%   $262.9886   $262.99   $263.00   $263.00  
  Purchase #3 $249.29   10.478%   $275.4106   $275.41   $275.40   $275.40  
  Purchase #4 $99.48   7.608%   $107.0484   $107.05   $107.05   $107.00  
  Purchase #5 $161.65   13.794%   $183.948   $183.95   $183.95   $183.90  
  Purchase #6 $22.50   11.411%   $25.0675   $25.07   $25.05   $25.10  
  Purchase #7 $5.99   10.173%   $6.5994   $6.60   $6.60   $6.60  
  7 purchase totals = $801.86       $895.7210   $895.73   $895.70   $895.70