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 $235.84   10.490%   $260.5796   $260.58   $260.60   $260.60  
  Purchase #2 $52.47   6.840%   $56.0589   $56.06   $56.05   $56.10  
  Purchase #3 $117.89   8.129%   $127.4733   $127.47   $127.45   $127.50  
  Purchase #4 $123.86   9.215%   $135.2737   $135.27   $135.25   $135.30  
  Purchase #5 $233.56   4.732%   $244.6121   $244.61   $244.60   $244.60  
  Purchase #6 $247.98   8.639%   $269.403   $269.40   $269.40   $269.40  
  Purchase #7 $193.55   6.746%   $206.6069   $206.61   $206.60   $206.60  
  7 purchase totals = $1,205.15       $1,300.0075   $1,300.00   $1,299.95   $1,300.10