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 $239.67   8.619%   $260.3272   $260.33   $260.35   $260.30  
  Purchase #2 $174.50   7.155%   $186.9855   $186.99   $187.00   $187.00  
  Purchase #3 $135.36   6.870%   $144.6592   $144.66   $144.65   $144.70  
  Purchase #4 $131.97   11.567%   $147.235   $147.24   $147.25   $147.20  
  Purchase #5 $227.65   5.661%   $240.5373   $240.54   $240.55   $240.50  
  Purchase #6 $135.27   4.361%   $141.1691   $141.17   $141.15   $141.20  
  Purchase #7 $107.91   3.240%   $111.4063   $111.41   $111.40   $111.40  
  7 purchase totals = $1,152.33       $1,232.3196   $1,232.34   $1,232.35   $1,232.30