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 $57.38   8.193%   $62.0811   $62.08   $62.10   $62.10  
  Purchase #2 $78.28   7.117%   $83.8512   $83.85   $83.85   $83.90  
  Purchase #3 $119.57   12.470%   $134.4804   $134.48   $134.50   $134.50  
  Purchase #4 $195.69   4.631%   $204.7524   $204.75   $204.75   $204.80  
  Purchase #5 $28.87   5.720%   $30.5214   $30.52   $30.50   $30.50  
  Purchase #6 $68.91   6.262%   $73.2251   $73.23   $73.25   $73.20  
  Purchase #7 $153.93   6.107%   $163.3305   $163.33   $163.35   $163.30  
  7 purchase totals = $702.63       $752.2421   $752.24   $752.30   $752.30