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 $186.77   11.130%   $207.5575   $207.56   $207.55   $207.60  
  Purchase #2 $216.27   8.862%   $235.4358   $235.44   $235.45   $235.40  
  Purchase #3 $136.53   3.791%   $141.7059   $141.71   $141.70   $141.70  
  Purchase #4 $239.48   11.748%   $267.6141   $267.61   $267.60   $267.60  
  Purchase #5 $60.49   8.785%   $65.804   $65.80   $65.80   $65.80  
  Purchase #6 $172.27   5.466%   $181.6863   $181.69   $181.70   $181.70  
  Purchase #7 $245.79   7.816%   $265.0009   $265.00   $265.00   $265.00  
  7 purchase totals = $1,257.60       $1,364.8045   $1,364.81   $1,364.80   $1,364.80