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 $66.66   3.350%   $68.8931   $68.89   $68.90   $68.90  
  Purchase #2 $234.88   11.675%   $262.3022   $262.30   $262.30   $262.30  
  Purchase #3 $126.96   7.207%   $136.11   $136.11   $136.10   $136.10  
  Purchase #4 $131.70   12.108%   $147.6462   $147.65   $147.65   $147.60  
  Purchase #5 $40.27   10.125%   $44.3473   $44.35   $44.35   $44.30  
  Purchase #6 $239.92   10.610%   $265.3755   $265.38   $265.40   $265.40  
  Purchase #7 $216.91   4.597%   $226.8814   $226.88   $226.90   $226.90  
  7 purchase totals = $1,057.30       $1,151.5557   $1,151.56   $1,151.60   $1,151.50