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 $176.32   12.543%   $198.4358   $198.44   $198.45   $198.40  
  Purchase #2 $215.55   3.716%   $223.5598   $223.56   $223.55   $223.60  
  Purchase #3 $128.89   3.226%   $133.048   $133.05   $133.05   $133.00  
  Purchase #4 $7.63   8.255%   $8.2599   $8.26   $8.25   $8.30  
  Purchase #5 $243.77   7.767%   $262.7036   $262.70   $262.70   $262.70  
  Purchase #6 $170.34   6.518%   $181.4428   $181.44   $181.45   $181.40  
  Purchase #7 $49.76   9.668%   $54.5708   $54.57   $54.55   $54.60  
  7 purchase totals = $992.26       $1,062.0207   $1,062.02   $1,062.00   $1,062.00