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 $14.48   3.238%   $14.9489   $14.95   $14.95   $14.90  
  Purchase #2 $152.67   6.787%   $163.0317   $163.03   $163.05   $163.00  
  Purchase #3 $81.40   4.318%   $84.9149   $84.91   $84.90   $84.90  
  Purchase #4 $56.52   12.244%   $63.4403   $63.44   $63.45   $63.40  
  Purchase #5 $62.80   13.692%   $71.3986   $71.40   $71.40   $71.40  
  Purchase #6 $216.46   10.166%   $238.4653   $238.47   $238.45   $238.50  
  Purchase #7 $73.72   4.613%   $77.1207   $77.12   $77.10   $77.10  
  7 purchase totals = $658.05       $713.3204   $713.32   $713.30   $713.20