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 $66.99   13.329%   $75.9191   $75.92   $75.90   $75.90  
  Purchase #2 $219.55   8.235%   $237.6299   $237.63   $237.65   $237.60  
  Purchase #3 $158.52   5.698%   $167.5525   $167.55   $167.55   $167.60  
  Purchase #4 $30.65   7.693%   $33.0079   $33.01   $33.00   $33.00  
  Purchase #5 $246.32   3.280%   $254.3993   $254.40   $254.40   $254.40  
  Purchase #6 $142.26   4.305%   $148.3843   $148.38   $148.40   $148.40  
  Purchase #7 $31.75   4.353%   $33.1321   $33.13   $33.15   $33.10  
  7 purchase totals = $896.04       $950.0251   $950.02   $950.05   $950.00