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 $191.27   8.128%   $206.8164   $206.82   $206.80   $206.80  
  Purchase #2 $179.26   10.201%   $197.5463   $197.55   $197.55   $197.50  
  Purchase #3 $25.85   9.768%   $28.375   $28.38   $28.40   $28.40  
  Purchase #4 $5.41   7.717%   $5.8275   $5.83   $5.85   $5.80  
  Purchase #5 $91.25   4.179%   $95.0633   $95.06   $95.05   $95.10  
  Purchase #6 $127.95   13.668%   $145.4382   $145.44   $145.45   $145.40  
  Purchase #7 $228.76   7.667%   $246.299   $246.30   $246.30   $246.30  
  7 purchase totals = $849.75       $925.3657   $925.38   $925.40   $925.30