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 $68.66   11.807%   $76.7667   $76.77   $76.75   $76.80  
  Purchase #2 $110.31   7.512%   $118.5965   $118.60   $118.60   $118.60  
  Purchase #3 $35.43   10.848%   $39.2734   $39.27   $39.25   $39.30  
  Purchase #4 $193.32   3.657%   $200.3897   $200.39   $200.40   $200.40  
  Purchase #5 $212.59   6.196%   $225.7621   $225.76   $225.75   $225.80  
  Purchase #6 $11.69   4.865%   $12.2587   $12.26   $12.25   $12.30  
  Purchase #7 $176.60   11.853%   $197.5324   $197.53   $197.55   $197.50  
  7 purchase totals = $808.60       $870.5795   $870.58   $870.55   $870.70