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 $126.44   8.310%   $136.9472   $136.95   $136.95   $136.90  
  Purchase #2 $97.92   8.428%   $106.1727   $106.17   $106.15   $106.20  
  Purchase #3 $118.65   7.264%   $127.2687   $127.27   $127.25   $127.30  
  Purchase #4 $219.69   5.451%   $231.6653   $231.67   $231.65   $231.70  
  Purchase #5 $227.78   9.240%   $248.8269   $248.83   $248.85   $248.80  
  Purchase #6 $144.56   6.503%   $153.9607   $153.96   $153.95   $154.00  
  Purchase #7 $5.61   13.347%   $6.3588   $6.36   $6.35   $6.40  
  7 purchase totals = $940.65       $1,011.2003   $1,011.21   $1,011.15   $1,011.30