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 $150.79   5.486%   $159.0623   $159.06   $159.05   $159.10  
  Purchase #2 $163.53   3.804%   $169.7507   $169.75   $169.75   $169.80  
  Purchase #3 $59.86   13.521%   $67.9537   $67.95   $67.95   $68.00  
  Purchase #4 $17.28   3.774%   $17.9321   $17.93   $17.95   $17.90  
  Purchase #5 $243.97   13.109%   $275.952   $275.95   $275.95   $276.00  
  Purchase #6 $191.35   13.703%   $217.5707   $217.57   $217.55   $217.60  
  Purchase #7 $183.63   6.233%   $195.0757   $195.08   $195.10   $195.10  
  7 purchase totals = $1,010.41       $1,103.2972   $1,103.29   $1,103.30   $1,103.50