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 $29.46   11.208%   $32.7619   $32.76   $32.75   $32.80  
  Purchase #2 $232.51   8.522%   $252.3245   $252.32   $252.30   $252.30  
  Purchase #3 $11.43   12.556%   $12.8652   $12.87   $12.85   $12.90  
  Purchase #4 $246.58   13.476%   $279.8091   $279.81   $279.80   $279.80  
  Purchase #5 $185.25   10.590%   $204.868   $204.87   $204.85   $204.90  
  Purchase #6 $132.76   11.280%   $147.7353   $147.74   $147.75   $147.70  
  Purchase #7 $20.54   12.418%   $23.0907   $23.09   $23.10   $23.10  
  7 purchase totals = $858.53       $953.4547   $953.46   $953.40   $953.50