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 $181.38   13.564%   $205.9824   $205.98   $206.00   $206.00  
  Purchase #2 $23.27   4.849%   $24.3984   $24.40   $24.40   $24.40  
  Purchase #3 $109.52   5.309%   $115.3344   $115.33   $115.35   $115.30  
  Purchase #4 $26.99   9.825%   $29.6418   $29.64   $29.65   $29.60  
  Purchase #5 $128.90   10.218%   $142.071   $142.07   $142.05   $142.10  
  Purchase #6 $110.27   4.522%   $115.2564   $115.26   $115.25   $115.30  
  Purchase #7 $55.64   13.405%   $63.0985   $63.10   $63.10   $63.10  
  7 purchase totals = $635.97       $695.7829   $695.78   $695.80   $695.80