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 $67.99   4.356%   $70.9516   $70.95   $70.95   $71.00  
  Purchase #2 $206.25   12.656%   $232.353   $232.35   $232.35   $232.40  
  Purchase #3 $166.84   5.329%   $175.7309   $175.73   $175.75   $175.70  
  Purchase #4 $184.99   11.729%   $206.6875   $206.69   $206.70   $206.70  
  Purchase #5 $83.35   6.182%   $88.5027   $88.50   $88.50   $88.50  
  Purchase #6 $38.51   4.133%   $40.1016   $40.10   $40.10   $40.10  
  Purchase #7 $165.83   12.326%   $186.2702   $186.27   $186.25   $186.30  
  7 purchase totals = $913.76       $1,000.5975   $1,000.59   $1,000.60   $1,000.70