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 $79.38   8.781%   $86.3504   $86.35   $86.35   $86.40  
  Purchase #2 $149.42   12.189%   $167.6328   $167.63   $167.65   $167.60  
  Purchase #3 $35.64   8.381%   $38.627   $38.63   $38.65   $38.60  
  Purchase #4 $239.76   9.601%   $262.7794   $262.78   $262.80   $262.80  
  Purchase #5 $29.70   13.388%   $33.6762   $33.68   $33.70   $33.70  
  Purchase #6 $203.80   9.507%   $223.1753   $223.18   $223.20   $223.20  
  Purchase #7 $123.53   5.228%   $129.9881   $129.99   $130.00   $130.00  
  7 purchase totals = $861.23       $942.2292   $942.24   $942.35   $942.30