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 $67.76   5.822%   $71.705   $71.71   $71.70   $71.70  
  Purchase #2 $249.71   13.316%   $282.9614   $282.96   $282.95   $283.00  
  Purchase #3 $129.65   8.578%   $140.7714   $140.77   $140.75   $140.80  
  Purchase #4 $225.94   4.250%   $235.5425   $235.54   $235.55   $235.50  
  Purchase #5 $201.55   4.509%   $210.6379   $210.64   $210.65   $210.60  
  Purchase #6 $13.86   7.160%   $14.8524   $14.85   $14.85   $14.90  
  Purchase #7 $70.28   9.801%   $77.1681   $77.17   $77.15   $77.20  
  7 purchase totals = $958.75       $1,033.6387   $1,033.64   $1,033.60   $1,033.70