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 $58.44   8.826%   $63.5979   $63.60   $63.60   $63.60  
  Purchase #2 $161.80   10.448%   $178.7049   $178.70   $178.70   $178.70  
  Purchase #3 $247.66   8.443%   $268.5699   $268.57   $268.55   $268.60  
  Purchase #4 $136.96   6.713%   $146.1541   $146.15   $146.15   $146.20  
  Purchase #5 $84.66   8.656%   $91.9882   $91.99   $92.00   $92.00  
  Purchase #6 $178.67   3.703%   $185.2862   $185.29   $185.30   $185.30  
  Purchase #7 $122.59   13.808%   $139.5172   $139.52   $139.50   $139.50  
  7 purchase totals = $990.78       $1,073.8184   $1,073.82   $1,073.80   $1,073.90