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 $145.38   11.343%   $161.8705   $161.87   $161.85   $161.90  
  Purchase #2 $102.91   8.545%   $111.7037   $111.70   $111.70   $111.70  
  Purchase #3 $144.72   12.620%   $162.9837   $162.98   $163.00   $163.00  
  Purchase #4 $242.72   6.727%   $259.0478   $259.05   $259.05   $259.00  
  Purchase #5 $97.30   6.520%   $103.644   $103.64   $103.65   $103.60  
  Purchase #6 $126.80   6.826%   $135.4554   $135.46   $135.45   $135.50  
  Purchase #7 $127.43   5.554%   $134.5075   $134.51   $134.50   $134.50  
  7 purchase totals = $987.26       $1,069.2126   $1,069.21   $1,069.20   $1,069.20