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 $216.46   8.682%   $235.2531   $235.25   $235.25   $235.30  
  Purchase #2 $181.89   11.106%   $202.0907   $202.09   $202.10   $202.10  
  Purchase #3 $214.34   7.591%   $230.6105   $230.61   $230.60   $230.60  
  Purchase #4 $154.80   7.171%   $165.9007   $165.90   $165.90   $165.90  
  Purchase #5 $15.49   11.267%   $17.2353   $17.24   $17.25   $17.20  
  Purchase #6 $235.43   12.417%   $264.6633   $264.66   $264.65   $264.70  
  Purchase #7 $161.56   12.387%   $181.5724   $181.57   $181.55   $181.60  
  7 purchase totals = $1,179.97       $1,297.3260   $1,297.32   $1,297.30   $1,297.40