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 $183.34   9.814%   $201.333   $201.33   $201.35   $201.30  
  Purchase #2 $114.88   3.264%   $118.6297   $118.63   $118.65   $118.60  
  Purchase #3 $199.79   13.773%   $227.3071   $227.31   $227.30   $227.30  
  Purchase #4 $184.59   5.691%   $195.095   $195.10   $195.10   $195.10  
  Purchase #5 $16.62   7.270%   $17.8283   $17.83   $17.85   $17.80  
  Purchase #6 $165.31   7.175%   $177.171   $177.17   $177.15   $177.20  
  Purchase #7 $17.32   3.846%   $17.9861   $17.99   $18.00   $18.00  
  7 purchase totals = $881.85       $955.3502   $955.36   $955.40   $955.30