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 $38.98   6.363%   $41.4603   $41.46   $41.45   $41.50  
  Purchase #2 $147.96   6.112%   $157.0033   $157.00   $157.00   $157.00  
  Purchase #3 $54.54   5.768%   $57.6859   $57.69   $57.70   $57.70  
  Purchase #4 $107.92   3.769%   $111.9875   $111.99   $112.00   $112.00  
  Purchase #5 $222.67   8.234%   $241.0046   $241.00   $241.00   $241.00  
  Purchase #6 $139.34   10.253%   $153.6265   $153.63   $153.65   $153.60  
  Purchase #7 $135.78   4.421%   $141.7828   $141.78   $141.80   $141.80  
  7 purchase totals = $847.19       $904.5509   $904.55   $904.60   $904.60