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 $62.52   8.719%   $67.9711   $67.97   $67.95   $68.00  
  Purchase #2 $144.66   9.826%   $158.8743   $158.87   $158.85   $158.90  
  Purchase #3 $243.58   7.795%   $262.5671   $262.57   $262.55   $262.60  
  Purchase #4 $182.69   4.362%   $190.6589   $190.66   $190.65   $190.70  
  Purchase #5 $137.57   3.250%   $142.041   $142.04   $142.05   $142.00  
  Purchase #6 $217.79   6.260%   $231.4237   $231.42   $231.40   $231.40  
  Purchase #7 $195.46   4.140%   $203.552   $203.55   $203.55   $203.60  
  7 purchase totals = $1,184.27       $1,257.0881   $1,257.08   $1,257.00   $1,257.20