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 $140.54   8.642%   $152.6855   $152.69   $152.70   $152.70  
  Purchase #2 $237.77   4.576%   $248.6504   $248.65   $248.65   $248.70  
  Purchase #3 $127.27   8.412%   $137.976   $137.98   $138.00   $138.00  
  Purchase #4 $248.95   7.505%   $267.6337   $267.63   $267.65   $267.60  
  Purchase #5 $113.41   6.354%   $120.6161   $120.62   $120.60   $120.60  
  Purchase #6 $189.26   3.634%   $196.1377   $196.14   $196.15   $196.10  
  Purchase #7 $158.42   11.804%   $177.1199   $177.12   $177.10   $177.10  
  7 purchase totals = $1,215.62       $1,300.8193   $1,300.83   $1,300.85   $1,300.80