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 $30.45   6.269%   $32.3589   $32.36   $32.35   $32.40  
  Purchase #2 $230.83   5.214%   $242.8655   $242.87   $242.85   $242.90  
  Purchase #3 $116.58   7.773%   $125.6418   $125.64   $125.65   $125.60  
  Purchase #4 $86.57   12.633%   $97.5064   $97.51   $97.50   $97.50  
  Purchase #5 $231.81   12.305%   $260.3342   $260.33   $260.35   $260.30  
  Purchase #6 $104.66   4.204%   $109.0599   $109.06   $109.05   $109.10  
  Purchase #7 $69.35   10.332%   $76.5152   $76.52   $76.50   $76.50  
  7 purchase totals = $870.25       $944.2819   $944.29   $944.25   $944.30