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 $151.68   13.422%   $172.0385   $172.04   $172.05   $172.00  
  Purchase #2 $209.38   13.508%   $237.6631   $237.66   $237.65   $237.70  
  Purchase #3 $61.81   6.287%   $65.696   $65.70   $65.70   $65.70  
  Purchase #4 $233.48   13.776%   $265.6442   $265.64   $265.65   $265.60  
  Purchase #5 $107.92   13.241%   $122.2097   $122.21   $122.20   $122.20  
  Purchase #6 $127.78   7.580%   $137.4657   $137.47   $137.45   $137.50  
  Purchase #7 $69.37   5.354%   $73.0841   $73.08   $73.10   $73.10  
  7 purchase totals = $961.42       $1,073.8013   $1,073.80   $1,073.80   $1,073.80