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 $119.39   13.150%   $135.0898   $135.09   $135.10   $135.10  
  Purchase #2 $233.64   4.289%   $243.6608   $243.66   $243.65   $243.70  
  Purchase #3 $76.59   13.472%   $86.9082   $86.91   $86.90   $86.90  
  Purchase #4 $110.46   7.152%   $118.3601   $118.36   $118.35   $118.40  
  Purchase #5 $149.37   6.725%   $159.4151   $159.42   $159.40   $159.40  
  Purchase #6 $152.29   9.866%   $167.3149   $167.31   $167.30   $167.30  
  Purchase #7 $148.95   5.717%   $157.4655   $157.47   $157.45   $157.50  
  7 purchase totals = $990.69       $1,068.2144   $1,068.22   $1,068.15   $1,068.30