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 $249.45   5.717%   $263.7111   $263.71   $263.70   $263.70  
  Purchase #2 $154.84   8.592%   $168.1439   $168.14   $168.15   $168.10  
  Purchase #3 $7.36   8.789%   $8.0069   $8.01   $8.00   $8.00  
  Purchase #4 $241.34   9.172%   $263.4757   $263.48   $263.50   $263.50  
  Purchase #5 $244.26   3.401%   $252.5673   $252.57   $252.55   $252.60  
  Purchase #6 $118.42   4.447%   $123.6861   $123.69   $123.70   $123.70  
  Purchase #7 $48.99   8.136%   $52.9758   $52.98   $53.00   $53.00  
  7 purchase totals = $1,064.66       $1,132.5668   $1,132.58   $1,132.60   $1,132.60