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 $214.57   8.487%   $232.7806   $232.78   $232.80   $232.80  
  Purchase #2 $187.38   6.228%   $199.05   $199.05   $199.05   $199.10  
  Purchase #3 $228.59   5.832%   $241.9214   $241.92   $241.90   $241.90  
  Purchase #4 $58.40   3.634%   $60.5223   $60.52   $60.50   $60.50  
  Purchase #5 $52.47   12.434%   $58.9941   $58.99   $59.00   $59.00  
  Purchase #6 $123.76   10.837%   $137.1719   $137.17   $137.15   $137.20  
  Purchase #7 $184.61   11.586%   $205.9989   $206.00   $206.00   $206.00  
  7 purchase totals = $1,049.78       $1,136.4392   $1,136.43   $1,136.40   $1,136.50